Rename split-loop-with-lambda to slice-with-lambda

The refactoring is now published as Slice on sammancoaching.org:
https://sammancoaching.org/refactorings/slice.html

- git mv ideas/split-loop-with-lambda -> ideas/slice-with-lambda
- rename learning-hour file and update frontmatter name
- update paths in tools/rehearse scripts and report title
- update prose: 'Split Loop with Lambda' -> 'Slice with Lambda'
  in learning hour, exercise READMEs, storyboard, solution comments
- link the published Slice refactoring from the pattern draft

ideas/slice-with-lambda/exercise/csharp/IceCreamShop.cs

@@ -0,0 +1,79 @@
+// Example 3 — Ice cream shop demo of Slice with Lambda (C#)
+//
+// Condensed mechanics: https://sammancoaching.org/refactorings/slice.html
+// (where that page says mock, we use a lambda instead).
+//
+// Third repetition, same complexity as ScheduleWatering in WeatherStation.cs
+// (guard -> one dependency call -> map to enum -> constant tail), so
+// participants can practice extracting a lambda a second time. The C#
+// delegate syntax is worth the repetition:
+//
+//     Func<byte> readTemperature = () => _thermometer.Read();
+//
+// Cast:
+//   Thermometer     — hardware-ish dependency. Read() returns a raw
+//                     byte value (not calibrated, the client decides
+//                     what it means).
+//   Warmth          — enum. Reading > 25 => Warm, otherwise Cold.
+//                     (Sunny/Shady's cousin from WeatherStation.cs.)
+//   ThawAmount      — enum. None / Medium / Low.
+//   IceCreamShop    — the client. Owns the _thawedToday flag, so the
+//                     guard is about client state, not sensor state.
+
+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 Thermometer _thermometer;
+    private bool _thawedToday;                      // event-style client state
+
+    public IceCreamShop(Thermometer thermometer)
+    {
+        _thermometer = thermometer;
+    }
+
+    public ThawAmount ThawStock()
+    {
+        if (_thawedToday)                           // guard: client state, stays
+        {
+            return ThawAmount.None;
+        }
+
+        _thawedToday = true;                        // set only after thawing
+        byte temperature = _thermometer.Read();     // middle: unwanted dependency
+        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;
+    }
+}