Do not close cached JarFile obtained from JarURLConnection

[aayushsrivastava]

What does this PR do?

CustomElementMatchers#readImplementationVersion closes the JarFile it uses to read a library's version unconditionally in its finally block. When the class's ProtectionDomain resolves to a JarURLConnection (the common case), JarURLConnection#getJarFile() returns a shared, cached JarFile instance by default (caching is on unless setUseCaches(false) was called), and per its contract that instance must not be closed by the caller.

Closing it breaks every other concurrent reader/classloader backed by the same cached JarFile. On Spring Boot executable jars this is severe: Boot's nested: protocol returns its shared cached NestedJarFile for a dependency jar, and that same instance also backs classloading for that jar. Closing it during a version-gated instrumentation check (e.g. the Mongo driver check) can fail concurrent classloads with NoClassDefFoundError and reads with ZipException: ZipFile closed, causing an intermittent startup crash.

Fixes #4541

This PR tracks whether the connection actually owns a private (non-cached) JarFile via JarURLConnection#getUseCaches(), and only closes it in that case. The new JarFile(file) branch (non-JarURLConnection case) is unaffected and is still always closed.

Checklist

• This is an enhancement of existing features, or a new feature in existing plugins
  • I have updated CHANGELOG.next-release.md
  • I have added tests that prove my fix is effective or that my feature works
  • Added an API method or config option? Document in which version this will be introduced
  • I have made corresponding changes to the documentation
• This is a bugfix
  • I have updated CHANGELOG.next-release.md
  • I have added tests that would fail without this fix
• This is a new plugin
  • I have updated CHANGELOG.next-release.md
  • My code follows the style guidelines of this project
  • I have made corresponding changes to the documentation
  • I have added tests that prove my fix is effective or that my feature works
  • New and existing unit tests pass locally with my changes
  • I have updated supported-technologies.md
  • Added an API method or config option? Document in which version this will be introduced
  • Added an instrumentation plugin? Describe how you made sure that old, non-supported versions are not instrumented by accident.
• This is something else
  • I have updated CHANGELOG.next-release.md

Note: only compiled apm-agent-plugin-sdk locally (./mvnw -pl apm-agent-plugin-sdk -am compile/test-compile, both clean); did not run the full test/verify suite locally, so CI should be the source of truth there.

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[aayushsrivastava]

Not needed anymore since #4543 fixes the same problem