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/java/README.md

@@ -0,0 +1,37 @@
+# IceCreamForecasting — Slice with Lambda (exercise)
+
+Pre-factored variant of [IceCreamForecasting-Refactoring-Kata](https://github.com/emilybache/IceCreamForecasting-Refactoring-Kata):
+the Q1/Q4 dead branch is stripped and the hardcoded dates are a constant now.
+Everything else — including the noise in the scoring loop — is untouched.
+
+## Task
+
+`longRangeForecast()` is hard to test: it calls `scorer`, and `Scorer`
+stands for an external weather service you must not call from a unit test.
+The rest of the method's inputs are only `DATES` and `ANCHOR_DATE`.
+
+Get it under test:
+
+1. First get any test running that calls `longRangeForecast()` —
+   it will fail or be flaky, because of the dependency on `Scorer`.
+2. Then use the **Slice with Lambda** mechanics (6 steps, on the handout)
+   so that the weather collection becomes an extracted method that takes the
+   weather-reading as a **lambda parameter**.
+3. Stop when you have an extracted method that takes the lambda as a parameter,
+   and a test that passes **without** touching `Scorer`.
+
+## Constraint
+
+Don't change `Scorer` and don't change the *behaviour* of
+`longRangeForecast()`. Compile early, compile often.
+
+## Debrief questions
+
+- At which step did plain **Split Loop** stop working, and why?
+  (Hint: what type did your introduced variable end up being?)
+- There are **two** calls to `scorer` in the weather loop.
+  What did you do with each one?
+- Could you delete either call without changing the forecast?
+  Try it. Why did that work?
+- Where would you take this next — more extraction, or moving the method
+  to another class where `Scorer` is unknown?