Implement deterministic RAND(N) and improve unseeded RAND() translation

[wp-fuse]

Summary

This PR improves the MySQL-compatible RAND() support in the AST-based SQLite driver. It replaces the previous generic implementation with a bit-exact MySQL Linear Congruential Generator (LCG) and a robust SQLite-level translation for unseeded calls.

Technical Changes

1. Seeded RAND(N):
   • Refactored the rand() UDF in WP_SQLite_PDO_User_Defined_Functions to use an instance-local LCG.
   • Implemented MySQL’s specific 30-bit seed initialization constants (0x10001, 55555555, 0x10000001) to ensure bit-exact deterministic output for given seeds, as requested in the previous review.
   • Removed mt_srand() and mt_rand() usage to prevent PHP global state pollution.
2. Unseeded RAND():
   • Updated the AST node translation in WP_PDO_MySQL_On_SQLite to use:
     ((RANDOM() & 0x7FFFFFFFFFFFFFFF) / 9223372036854775808.0).
   • This bitwise approach avoids integer overflow issues inherent to ABS(-9223372036854775808) in SQLite and ensures an unbiased distribution in the [0, 1) range.
3. Cleanup: This is a standalone PR following the feedback to separate the RAND() fix from other compatibility layers. All string-replacement hacks and non-AST layers have been excluded.

Validation

• PHPUnit: All 795 tests in the official test suite are passing.
• CS: Verified against WordPress Coding Standards via phpcs.