Play Framework

chore(classloading): drop ContinuationEnhancer + EnhancedForContinuations

Step 3/4 toward eliminating Javaflow. Deletes the bytecode enhancer that
ContinuationEnhancer wove around every action method to enable Javaflow's
StackRecorder hand-off, plus the marker-class EnhancedForContinuations and
the now-orphaned ContinuationsException type.

Removes:
- framework/src/play/classloading/enhancers/ContinuationEnhancer.java (113 lines)
- framework/src/play/classloading/enhancers/EnhancedForContinuations.java (8 lines)
- framework/src/play/exceptions/ContinuationsException.java
- ContinuationEnhancer's slot in EnhancerPlugin.defaultEnhancers — the chain
  is now PropertiesEnhancer, SigEnhancer, ControllersEnhancer, MailerEnhancer,
  LocalvariablesNamesEnhancer.

Side benefit: faster classloader pipeline. Every loaded application class
used to traverse ContinuationEnhancer's bytecode rewrite (BCI scan + frame
analysis) even though only @action methods would have benefited; that pass
is gone now.

ant unittest passes; the commons-javaflow jar dependency remains and is
deleted in the next commit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>