(feat) O3-5064: Implement thread-safe session registry and REST endpoints for Drools sessions

[UjjawalPrabhat]

Summary

Implements a thread-safe session registry for Drools auto-start sessions, enabling REST-based querying of existing stateful sessions as requested in O3-5064.

Key Changes

New Components:

• SessionRegistry - Interface for session management (register, checkout, exists, remove)
• SessionRegistryImpl - Thread-safe implementation using ConcurrentHashMap + per-session ReentrantLock
• SessionLease - AutoCloseable wrapper for thread-safe session checkout
• SessionRegistryTest - 16 comprehensive tests

Service Integration:

• Added SessionRegistry as private field in DroolsEngineServiceImpl (service encapsulation)
• Added 3 service methods: registerAutoStartSession(), checkOutAutoStartSession(), isSessionRegistered()
• Modified requestSession() to check registry for auto-start sessions before creating new ones

Module Startup:

• DroolsEngineRunner now registers auto-start sessions after creation via registerAutoStartSession()

How It Works?

Startup: Auto-start sessions created → fired → registered in registry
REST Request: Check if auto-start + registered → reuse from registry (thread-safe) OR create new session

Related Issue

O3-5064

Related PR

[UjjawalPrabhat]

@ibacher @samuelmale Could you please review this PR?