Slice with lambda: add C# exercise projects and export

- Add SliceWithLambda.slnx + csproj scaffolding for ideas/slice-with-lambda/
  exercise/csharp (examples project + xUnit solution/test project)
- Add exercises/slice-with-lambda (C# version of the prefactored-longrange
  exercise with Buyers and SliceWithLambda projects)
- Add export/slice-with-lambda (nested git repo with exercise export)
- Ignore bin/ and obj/ build output at repo root

exercises/slice-with-lambda/solution/SliceWithLambda/IceCreamShopSolution.cs

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+// Example 3 solution — Ice cream shop demo of Slice with Lambda (C#), after
+//
+// Lambda extracted (step 1), slid to the top (step 2), method extracted
+// below the guard (step 3). The constructor now takes the lambda directly,
+// so tests construct with new IceCreamShop(() => 30).
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+
+using System;
+
+public enum Warmth
+{
+    Cold,
+    Warm
+}
+
+public enum ThawAmount
+{
+    None,
+    Medium,
+    Low
+}
+
+public class Thermometer
+{
+    private readonly Random _rng = new Random();    // stand-in for the hardware
+
+    public byte Read()
+    {
+        return (byte)_rng.Next(50);                 // raw sensor value
+    }
+}
+
+public class IceCreamShop
+{
+    private readonly Func<byte> _readTemperature;   // the thermometer, as a lambda
+    private bool _thawedToday;                      // event-style client state
+
+    public IceCreamShop(Func<byte> readTemperature)
+    {
+        _readTemperature = readTemperature;
+    }
+
+    public ThawAmount ThawStock()
+    {
+        Func<byte> readTemperature = () => _readTemperature();  // lambda at the top
+        return ThawStockTail(readTemperature);      // pass the lambda on
+    }
+
+    private ThawAmount ThawStockTail(Func<byte> readTemperature)
+    {
+        if (_thawedToday)                           // guard: client state, stays
+        {
+            return ThawAmount.None;
+        }
+
+        _thawedToday = true;                        // set only after thawing
+        byte temperature = readTemperature();       // middle: the stubbed lambda
+        Warmth warmth = ToWarmth(temperature);
+        if (warmth == Warmth.Warm)                  // tail: complex behaviour below
+        {                                           // the extraction point
+            return ThawAmount.Medium;
+        }
+        return ThawAmount.Low;
+    }
+
+    private static Warmth ToWarmth(byte temperature)
+    {
+        return temperature > 25 ? Warmth.Warm : Warmth.Cold;
+    }
+}

exercises/slice-with-lambda/solution/SliceWithLambda/MetaphorFreeSolution.cs

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+// Example 1 solution — Metaphor-free demo of Slice with Lambda (C#), after
+//
+// Lambda extracted (step 1), slid to the top (step 2), method extracted
+// below the guard (step 3), overload seam added (step 3b), b inlined
+// (final cleanup).
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+
+using System;
+
+public class Calculator
+{
+    private readonly SomeDependency _someDependency;
+
+    public Calculator(SomeDependency someDependency)
+    {
+        _someDependency = someDependency;
+    }
+
+    public int Calculate(int a)                          // overload: callers unchanged
+    {
+        return Calculate(a, a =>
+            _someDependency.mightThrowWhenPreconditionNotSatisfied(a));
+    }                                                    //   the real λ, baked into the head
+
+    public int Calculate(int a, Func<int, int> readB)    // the seam: λ is a parameter
+    {
+        if (a < 0) return 0;                             // guard clause: stays
+        return CalculateTail(a, readB);
+    }
+
+    private int CalculateTail(int a, Func<int, int> readB)
+    {
+        int c = a + readB(a);                            // b inlined
+        return c * 2;
+    }
+}
+
+public class SomeDependency
+{
+    private readonly Random _rng = new Random();    // stand-in for unpredictable computation
+
+    public int mightThrowWhenPreconditionNotSatisfied(int a)
+    {
+        if (a > 99)
+        {
+            throw new InvalidOperationException("precondition not satisfied");
+        }
+        return _rng.Next(100);
+    }
+}

exercises/slice-with-lambda/solution/SliceWithLambda/SliceWithLambda.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

exercises/slice-with-lambda/solution/SliceWithLambda/WeatherStationSolution.cs

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+// Example 2 solution — Weather Station domain demo of Slice with Lambda (C#), after
+//
+// Lambda extracted (step 1), slid to the top (step 2), method extracted
+// below the guard (step 3). The constructor now takes the lambda directly,
+// so tests construct with new SprinklerController(() => 200).
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+
+using System;
+
+public enum SunExposure
+{
+    Shady,
+    Sunny
+}
+
+public enum WateringDuration
+{
+    None,
+    Medium,
+    Short
+}
+
+public class LightSensor
+{
+    private readonly Random _rng = new Random();    // stand-in for hardware noise
+
+    public byte Read()
+    {
+        return (byte)_rng.Next(256);
+    }
+}
+
+public class SprinklerController
+{
+    private readonly Func<byte> _readLight;         // the sensor, as a lambda
+    private bool _wateredToday;                     // event-style client state
+
+    public SprinklerController(Func<byte> readLight)
+    {
+        _readLight = readLight;
+    }
+
+    public WateringDuration ScheduleWatering()
+    {
+        Func<byte> readLight = () => _readLight();  // lambda definition at the top
+        return ScheduleWateringTail(readLight);     // pass the lambda on
+    }
+
+    private WateringDuration ScheduleWateringTail(Func<byte> readLight)
+    {
+        if (_wateredToday)                          // guard: client state, stays
+        {
+            return WateringDuration.None;
+        }
+
+        _wateredToday = true;                       // set only after watering
+        byte reading = readLight();                 // middle: the stubbed lambda
+        SunExposure exposure = ToSunExposure(reading);
+        if (exposure == SunExposure.Sunny)          // tail: complex behaviour below
+        {                                           // the extraction point
+            return WateringDuration.Medium;
+        }
+        return WateringDuration.Short;
+    }
+
+    private static SunExposure ToSunExposure(byte reading)
+    {
+        return reading > 128 ? SunExposure.Sunny : SunExposure.Shady;
+    }
+}