RecipeSpec recipe caching

[nmck257]

What's changed?

RecipeSpec methods recipeFromYaml, recipeFromResource, and recipeFromResources now memoize Recipes to avoid repeated redundant Environment instantiation / classpath scanning

What's your motivation?

Speed of unit tests; these methods (especially when calling scanYamlResources) can cost a few hundred milliseconds, which adds up fast if a large test class is using them.

Have you considered any alternatives or workarounds?

• For a lighter touch, we could store only the Environment built with the scanYamlResources call in a lazy-init static field; this probably delivers ~most of the speed benefits with less code and less mem
• Using a memoization/caching library might be nicer, but, at the cost of another dependency
• Hashing together the relevant Strings (instead of joining them) might make for cheaper keys, but I struggled to implement that concisely since doing fancy stuff with varargs is a bit painful in java (no spread operator), esp 8 (fewer helper methods for instantiating lists, etc)
• I tried caching the customized testClassSpec objects used by rewriteRun, but that was impractical since RewriteTest is an interface and can't support instance variables
• A step further on the above, I even experimented with a static WeakHashMap<Consumer<RecipeSpec>, RecipeSpec> to cache testClassSpec objects based on the customizer (eg this::defaults) which would produce them, but I couldn't get keys with consistent memory references. And even if I could figure out clever lambda syntax to make that happen, it would depend on the test class being configured to as TestInstanceLifecycle(PER_CLASS), which is non-default and has other ramifications

Any additional context

Checklist

• I've added unit tests to cover both positive and negative cases
• I've added the license header to any new files through ./gradlew licenseFormat
• I've used the IntelliJ IDEA auto-formatter on affected files

[nmck257]

test failures look unrelated (something about the rewrite-gradle model failing to resolve the rewrite-core:8.8.0-SNAPSHOT dep)

[sambsnyd]

Thanks @nmck257 !