Fix GH-20262: array_unique() SORT_REGULAR fails to deduplicate with mixed strings

[jmarble]

The Bug

array_unique() with SORT_REGULAR was failing to remove duplicate numeric strings when mixed with alphanumeric strings:

$units = ['5', '10', '3A', '5'];
array_unique($units, SORT_REGULAR);
// Before: ['5', '10', '3A', '5'] - duplicate '5' not removed 
// After:  ['5', '10', '3A']      - works correctly 

Root Cause

Non-transitive comparisons in SORT_REGULAR (where '5' == 5 and 5 != '5abc' but '5' < '5abc') broke the sort-based algorithm's assumption that sorting would group duplicates adjacently.

Solution

Implemented type-optimized hybrid approach for SORT_REGULAR:

Three-tier algorithm selection:

1. Integer-only arrays: O(N) hash table for optimal performance
2. Arrays/Objects present: O(N log N) sort-based deduplication (existing algorithm)
3. Mixed scalar types: O(N) hash bucketing with type-aware hashing and SORT_REGULAR comparison

Performance

Improved performance across all data types compared to PHP 8.4.13 while fixing correctness issues.

Backward Compatibility

• 100% BC compatible - preserves all existing coercion behavior
• Uses identical comparison functions as current implementation
• All existing tests pass (834/834)

Tests Added

• gh20262.phpt - Minimal regression test for the bug
• array_unique_variation_sort_regular.phpt - Comprehensive SORT_REGULAR behavior coverage (16 scenarios)

[jmarble]

Another variation of the example bug, but using objects:
https://3v4l.org/5kr1t

My PR does not make an attempt to resolve this issue with complex types.

[jmarble]

Closing in favor of #20305 which provides a complete solution that fixes transitivity for all mixed types (scalars, nested arrays, and objects).