Play Framework

test(classloading): add bytecode-enhancer + precompiled-guard tests (PF-136)

framework/src/play/classloading/ had zero direct tests. Add real behavioral
tests that enhance compiled fixture bytecode, load the enhanced class, and
exercise it:

- PropertiesEnhancer: generated getX/setX round-trip + @PlayPropertyAccessor
  stamp; direct field access rewritten through FieldAccessor.invoke{Read,Write}Property.
- LocalvariablesNamesEnhancer: method parameter names recoverable from the
  LocalVariablesNamesTracer registry at runtime; enter()/exit() balance.
- ApplicationClasses.enhance() isTestSource() gate: under -Dprecompile an
  app-rooted class IS written to precompiled/java/ but a test-rooted class is
  NOT (keeps test code + JUnit off the prod classpath).

Each test has a paired UN-enhanced/negative assertion as a built-in mutation
check. Test-only; no production changes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>