LDEV-6240 skip findLoadedClass in EnvClassLoader, clear callerCache on RPC flush

[zspitzer]

Summary

• Remove findLoadedClass() from EnvClassLoader.loadClass() — it returns classes from the JVM's internal cache which cannot be cleared after a PhysicalClassLoader flush
• Add clearCallerCache() to EnvClassLoader and call it from PhysicalClassLoader.flush() for RPC classloaders
• After flush, stale classes from the old classloader caused isAssignableFrom failures in ServiceLoader and other JDK code

https://luceeserver.atlassian.net/browse/LDEV-6240

Detail

When a library loaded via JavaSettings (RPC PhysicalClassLoader) uses ServiceLoader.load(), the thread context classloader (EnvClassLoader) loads the SPI implementation class by delegating to the RPC PCL on the call stack. The JVM caches this in findLoadedClass() permanently.

After PCL flush (idle eviction, reinit, or rename ratio), a new PCL is created. New code loads the SPI interface from the new PCL, but EnvClassLoader.findLoadedClass() still returns the old implementation class. ServiceLoader checks isAssignableFrom between the two → fails → "not a subtype".

Fix: skip findLoadedClass() entirely (rely on callerCache which we control and can clear), and clear callerCache on RPC flush.

Test plan

• test/tickets/LDEV6240.cfc — 5 tests all passing
• Test 4 auto-detects whether clearCallerCache() exists and verifies it works