[WIP] Update jmx-metrics module to follow style guide

[Copilot]

• Identify all public classes that need to be declared final
• Remove final modifier from method parameters and local variables
• Check and improve static imports usage where applicable
• Verify class organization follows style guide order
• Run tests to ensure no breaking changes
• Apply spotless formatting

Analysis shows the main style guide violations in jmx-metrics module are:

1. Public classes not declared final (GroovyRunner, JmxClient, GroovyMetricEnvironment, ConfigurationException, JmxConnectorHelper, ClientCallbackHandler)
2. Method parameters and local variables declared final (violates style guide)
3. Potential improvements to static imports

Fixes #391.

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