security: update pgx/v5 to v5.9.2 (critical)

[coffeegoddd]

Summary

• Updates github.com/jackc/pgx/v5 from v5.6.1-0.20240826124046 to v5.9.2
• Fixes Dependabot alert Zachmu/err handling repro #54 (critical: memory-safety vulnerability, CVE-2026-33816)
• Fixes Dependabot alert Parser Tests Tool #58 (low: SQL injection via placeholder confusion)
• No code changes needed — clean upgrade

Test plan

• CI passes
• Postgres client integration tests pass

🤖 Generated with Claude Code

[coffeegoddd]

Closing in favor of Dependabot PR #2654 which covers the same pgx/v5 upgrade.

[github-actions]

	Main	PR
covering_index_scan_postgres	1293.07/s	${\color{red}DNF}$
index_join_postgres	194.59/s	${\color{red}DNF}$
index_join_scan_postgres	207.49/s	${\color{red}DNF}$
index_scan_postgres	11.78/s	${\color{red}DNF}$
oltp_point_select	2298.15/s	${\color{red}DNF}$
oltp_read_only	1839.43/s	${\color{red}DNF}$
select_random_points	130.32/s	${\color{red}DNF}$
select_random_ranges	1054.01/s	${\color{red}DNF}$
table_scan_postgres	11.49/s	${\color{red}DNF}$
types_table_scan_postgres	5.25/s	${\color{red}DNF}$