[PATCH] Implement dynamic predicate lock ratio limits

Hi hackers,

This patch series implements the TODO in predicate.c that suggests adding
ratio-based predicate lock limits.

The series is split into two logical commits:

1. Core implementation of the GUC variables and predicate lock logic
2. Comprehensive regression tests

Patch overview:
- Adds max_predicate_locks_per_relation_ratio and
max_predicate_locks_per_page_ratio GUCs
- When ratios are > 0, calculates lock limits based on relation size estimates
- Maintains full backward compatibility (default 0.0 = use existing
fixed limits)
- Includes complete regression test coverage

This addresses the TODO comment in MaxPredicateChildLocks() for more
intelligent lock allocation in mixed workloads.

Looking forward to your review!

ArkadySkv