fix(spi): 9 fixes for connection pool, SQL execution, and context

[HandSonic]

Summary

Fixes 9 verified bugs in the SPI core layer.

Fixes included:

• SqlUtils.count(): wrong variable s.length() → countSql.length() in substring (CRITICAL)
• MySQL buildExt(): returned getComment() instead of getExtent() (CRITICAL)
• SQL Server buildTableName(): checked databaseName twice instead of schemaName (CRITICAL)
• DefaultDBManager: empty catch blocks on setCatalog()/setSchema() now log warnings
• ConnectionPool cleanup: added iterator.remove() after closing dead connections
• ConnectionPool.getConnection: returns ConnectInfo to queue when trySetInUse() fails
• ConnectInfo.hashCode(): aligned with equals() fields {dataSourceId, gmtModified}
• fetchAllTableRecords: added rollback in catch, autoCommit restore in finally, ResultSet in try-with-resources
• count() ResultSet: now in try-with-resources
• Chat2DBContext: throws descriptive error for unknown dbType

[openai0229]

Please split this PR into focused changes. It currently bundles nine unrelated fixes across connection-pool concurrency, transaction state, SQL generation, SQL Server schema handling, equality/hash behavior, and plugin lookup. These areas have different failure modes and need independent tests and rollback boundaries.

In particular, please add concurrency coverage for connection cleanup/queue behavior; preserve and restore the caller's original autoCommit state instead of forcing true; and test commit/rollback behavior around connection failures. The MySQL extent, SQL Server schema, equals/hashCode, and plugin lookup changes also need focused coverage.

The count SQL fix overlaps #1966. Please remove it here and let the smaller #1966 land independently.

[HandSonic]

Updated the PR per review feedback:

1. Removed SqlUtils count fix — overlaps Fix count SQL semicolon trimming #1966, skipped during rebase
2. Fixed autoCommit restore — now saves connection.getAutoCommit() before modifying and restores the original value in finally, instead of forcing true
3. Rebased on current main — reduced from 9 to 8 commits, 7 files changed

The remaining focused changes are:

• MySQL buildExt() returns wrong value (1 line)
• SQL Server buildTableName() wrong condition (1 line)
• DefaultDBManager swallowed SQLException (2 lines)
• ConnectionPool cleanup + leak (5 lines)
• ConnectInfo hashCode alignment (1 line)
• fetchAllTableRecords rollback + autoCommit restore (25 lines)
• count() ResultSet leak (4 lines)
• Chat2DBContext null check (16 lines)