feature: add SQL monitoring and connection pool abstraction with implementation and tests

[Oscarcheng0312]

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Ⅰ. Describe what this PR did

This PR introduces a complete SQL monitoring system and a connection pool abstraction with a concrete implementation, forming the foundation of the connection-pool in Seata.

1. SQL‑event collector (package org.apache.seata.common.monitor)
   • SqlExecutionEntry: immutable model of a single SQL execution event (sql, executionTimeMillis, holdTimeMillis, timestamp).
   • SqlMonitor: singleton collector that
     • records all SQL events (up to maxAllRecords)
     • records slow SQL events (execMs > slowThreshold) up to maxSlowEntries
     • exposes getAllRecords(), getSlowSqlList(), clearOldRecords(), resetForTest().
2. ConnectionPool (package org.apache.seata.common.pool)
   • ConnectionPoolConfig & ConnectionPoolMetrics: plain‐old‐Java objects representing connection‐pool metrics and config.
   • PoolManager: interface defining methods getConfig(), getMetrics(), updateConfig().
   • PoolManagerRegistry: simple lookup/factory returning a PoolManager instance by DataSource type.
3. Concrete Connection Pool Implementation
   • Adds actual implementation of PoolManager for supported pool types (e.g., Druid/Hikari) using reflection.
4. Unit Tests
   • SqlMonitorTest: Covers core monitor behaviors (recording, slow query detection, eviction, clear/reset)
   • Connection Pool Tests: Verifies the correctness of PoolManager implementations, metric reporting, and configuration updating.

Ⅱ. Does this pull request fix one issue?

No — this is a new feature for the common module and rm-datasource module, including features about SQL monitor for Druid, connection‐pool metrics config, and the implementation of the connection-pool.

Ⅲ. Why don't you add test cases (unit test/integration test)?

Unit tests are included for all core behaviors of SqlMonitor.
Connection pool implementation (config, metrics, update)

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews