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/solution/README.md

@@ -0,0 +1,27 @@
+# Reference solution — end state after step 3
+
+Derived from [IceCreamForecasting-Refactoring-Kata](https://github.com/emilybache/IceCreamForecasting-Refactoring-Kata)
+(same license as the kata applies to the copied `IceCream.java`).
+
+Run with `mvn test` — the approval test passes deterministically without
+touching the weather service.
+
+## What changed vs the exercise start
+
+1. Weather loop extracted to `collectExpectedWeather(LongFunction<Boolean>)`
+   — a static method whose only "unwanted dependency" is the lambda parameter.
+2. Public no-arg `longRangeForecast()` delegates to a new overload that takes
+   the weather function, keeping existing callers working.
+3. Test passes a pure lambda (`daysForward -> true`) — the original test
+   called the no-arg method and was flaky because of `Scorer`'s `Random`.
+
+## Variations to try (for the debrief or a second round)
+
+- `daysForward -> false` (no sunny holidays): scores drop to `+10` only.
+- `daysForward -> daysForward == 5` (exactly one sunny holiday, and it is not
+  `expectedWeather.get(1)`, so no `+2`): all flavours `10`.
+- Delete the `scorer.updateSelection()` call inside the production lambda:
+  the approved file does not change — the forecast never reads `Scorer.flavour`.
+- Variation end state: skip the overload; make `collectExpectedWeather`
+  package-private and test it directly with pure lambdas. Trade-off:
+  tests the pure slice but not the composition (scoring loop).