[WIP] Update jfr-connection module to follow style guide

[Copilot]

This PR updates the jfr-connection module to follow the OpenTelemetry Java Contrib style guide (docs/style-guide.md).

Analysis completed:

• Examine all Java files in the jfr-connection module
• Review style guide requirements systematically
• Identify violations to fix

Issues found and planned fixes:

• @nonnull annotation usage: RecordingOptions.java uses @Nonnull instead of @Nullable - should use consistent javax.annotation.Nullable
• Class finality: Several public classes should be declared final where possible
• Static imports: Test files should use static imports for commonly used AssertJ and test methods
• Test class visibility: Test classes should be package-protected (remove public modifiers if present)
• Class organization: Verify proper ordering of class members (static fields, instance fields, constructors, methods, nested classes)

Next steps:

• Implement static imports in test files
• Add final modifiers to appropriate public classes
• Fix annotation consistency
• Verify class organization follows style guide
• Run tests and formatting to ensure changes are minimal and correct

Fixes #204.

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