fix: multiple bug fixes and dead code cleanup

[hobostay]

Summary

• Go consumer fixes: Add missing Nack() method; use per-message nack for handler failures instead of skipping the entire batch; log warning for unregistered event types instead of silently dropping messages
• Security hardening: Use quote_ident() in maint() for VACUUM target; add explicit queue existence check in insert_event_raw() with clear error message
• Atomicity fix: dlq_replay_all() now wraps per-event replay in exception blocks so a single failure doesn't abort the entire operation
• Role hierarchy fix: upgrade_schema() had inverted role membership — pgque_admin was created as member of reader/writer instead of the reverse; also fixed return value (was hardcoded 0, now returns actual count)
• Dead code cleanup: Remove PG 8.3 pg_autovacuum code path (PgQue requires PG14+); remove references to non-existent schemas (pgq_ext, pgq_node, londiste, txid) from maint_tables_to_vacuum()
• Typo fixes: consubers→consumers, poin→point, oldes→oldest, wuith→with, accitentally→accidentally, Quete→Quote

Test plan

• Go code compiles and passes go vet
• Run existing SQL test suite against modified pgque.sql
• Verify upgrade_schema() role hierarchy is correct (pgque_reader → pgque_writer → pgque_admin)
• Test dlq_replay_all() with a concurrent queue drop to verify exception handling
• Verify insert_event_raw() raises clear error for non-existent queue

🤖 Generated with Claude Code

[NikolayS]

@hobostay thank you

It would be great to split this PR into pieces - I see two different classes things here:

1. Typos in the original PgQ code, as well as "dead code" (for pre-14) – we aim to keep the original code as unchanged as possible, incorporating it into a single .sql. I think it would be great to move typo fixes upstream: https://github.com/pgq/pgq
2. Everything else – I'm going to process separately

[hobostay]

@NikolayS Thank you for the feedback! I've updated the PR to remove all typo fixes and dead code cleanup (PG 8.3 pg_autovacuum code path, non-existent schema references in maint_tables_to_vacuum()). These changes have been reverted in commit 1830ca2.

This PR now only contains the substantive bug fixes:

• Go consumer: per-message nack for handler failures, log warning for unregistered event types
• Go client: add missing Nack() method
• dlq_replay_all(): wrap per-event replay in exception blocks
• maint(): use quote_ident() for VACUUM target
• upgrade_schema(): fix inverted role hierarchy, fix return value
• insert_event_raw(): add queue existence check with clear error message

I'll look into submitting the typo fixes upstream to pgq/pgq separately.