feat: preferred connection type pg only

[Rattenkrieg]

• Add targetServerType support for PostgreSQL multi-host connection pools, matching the semantics of pgjdbc's targetServerType and libpq's target_session_attrs;
• Revives Preferred server type connection factory #1064 which targeted 4.x; this implementation is redesigned for the 5.x ConnectionFactory architecture;
• Supports ANY, PRIMARY, SECONDARY, PREFER_PRIMARY, and PREFER_SECONDARY modes;
• Server type detection uses PG 14+ in_hot_standby GUC_REPORT (zero-cost, during handshake) with SHOW transaction_read_only fallback for older versions;

Differences from #1064

• Single shared factory instead of one ConnectionFactory per host - 5.x ConnectionFactory.connect() takes options per-call, so a ServerType[] array indexed by server position replaces per-factory state;
• Stale cache recovery - when all servers are skipped by cache, retries with cache disabled to force re-verification. Preferred server type connection factory #1064 had no cache invalidation, so failovers caused permanent misrouting;
• Connection leak on detection failure - if detectServerType fails after connect, the connection is explicitly closed before retrying. Preferred server type connection factory #1064 did not handle this path;
• Close-before-retry - mismatched connections are closed and the close is awaited before opening the next probe, matching pgjdbc behavior and ensuring PG connection slots are freed promptly;

Connection algorithm

The ServerTypeAwarePgConnectionFactory wraps PgConnectionFactory and manages a list of servers with round-robin selection:

• PRIMARY / SECONDARY (strict): Probes servers in round-robin order, returns the first match, closes mismatched connections. Fails with an error if no server of the desired type is found;
• PREFER_PRIMARY / PREFER_SECONDARY: Two-pass approach matching pgjdbc - strict pass first;
  (probe-and-close for mismatches), then falls back to connectToAny which accepts any reachable server regardless of type;
• ANY: Connects to the first reachable server with no type detection;