Add resource event listener extension point and Groovy callback

[mPokornyETM]

Summary

Introduces a ResourceEventListener extension point that fires events when lockable resources change state. A built-in GroovyCallbackListener evaluates a user-configured Groovy script on each event.

New features

• ResourceEventListener (ExtensionPoint): Java extension point for plugins to receive resource state change notifications
• GroovyCallbackListener: Built-in listener that evaluates a global Groovy callback script per event
• ResourceInfo: Immutable, sandbox-safe snapshot of a resource passed to Groovy scripts
• Async execution (default) with configurable timeout
• Events: LOCKED, UNLOCKED, RESERVED, UNRESERVED, STOLEN, REASSIGNED, RESET, RECYCLED, QUEUED

Configuration

Navigate to Manage Jenkins → System → Lockable Resources Manager → Resource Event Callback to configure the Groovy script, async mode, and timeout.

Binding variables in Groovy callback

Variable	Type	Description
\
esource\	\ResourceInfo\	Read-only snapshot of the affected resource
\event\	\String\	Event name (e.g. \LOCKED, \RESERVED)
\userName\	\String\	User who triggered the action
\�uildName\	\String\	Build display name

Testing

15 automated tests covering all event types, extension point registration, ResourceInfo snapshot correctness, Groovy callback execution (sync/async), and failure resilience.

Documentation

Added resource-event-notifications.md with usage examples.

Fixes #340
Fixes #676