fix(pg-cache): add error handler to prevent unhandled pool errors

[pyramation]

Summary

Adds an error handler to pg pools to prevent unhandled 'error' events from crashing Node.js when database connections are terminated during cleanup.

When pgpm test-packages runs dropDatabase to clean up test databases, it terminates all connections via pg_terminate_backend(). This causes idle pool connections to receive a 57P01 (admin_shutdown) error. Without an error handler, Node.js crashes and dumps the entire pg Client object to the console - producing hundreds of lines of useless output instead of a meaningful error message.

The fix:

• Attaches an error handler to each pool when created
• Logs expected cleanup errors (57P01) at debug level
• Logs unexpected errors at error level
• Prevents the unhandled error from crashing the process

Why this is safe (does NOT swallow real errors):
The handler only catches errors emitted on IDLE pooled connections via the EventEmitter pattern. Query errors (pool.query(), client.query()) are returned via Promise rejection and bubble up through async/await as normal exceptions - they are NOT affected by this handler.

Updates since last revision

Added extensive inline documentation explaining:

• Why the error handler exists (idle connection errors crash Node.js)
• Why it's safe (does NOT swallow query errors - those use Promise rejection)
• The two different error paths in pg-pool (query errors vs idle connection errors)
• When this handler fires (during pg_terminate_backend cleanup)
• PostgreSQL error codes handled (57P01 admin_shutdown)

Review & Testing Checklist for Human

• Review the inline documentation in pg.ts to verify the explanation of pg-pool's two error paths (Promise rejection for queries vs EventEmitter for idle connections) is accurate
• After merge, publish a new pgpm version and update constructive-db CI to use it
• Run pgpm test-packages in constructive-db to confirm the fix produces clean output

Test plan: After publishing the new pgpm version, re-run CI on constructive-db PR #108 and verify all modules pass without the pg Client object dump.

Notes

This is a companion fix for constructive-db PR #108 which replaces the custom test-all-packages.js script with pgpm test-packages.

Local testing confirmed: ran pgpm test-packages against constructive-db using the locally built pgpm with this fix - all 37 modules passed successfully.

Link to Devin run: https://app.devin.ai/sessions/ef6ccaafd0f44b358f6b529e50306865
Requested by: Dan Lynch ([email protected]) / @pyramation

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