Add PHPUnit tests workflow for Turso DB

[JanJakes]

Summary

Adds a CI job that runs the SQLite driver unit tests (packages/mysql-on-sqlite) against Turso DB, a Rust reimplementation of SQLite.

The workflow:

• Pins Turso main at commit 83d0f02f567f54ed9529f0b3955f294d3836a134 for reproducible builds.
• Applies the Turso source patches listed below.
• Builds the turso_sqlite3 crate as a shared library and verifies its exported SQLite C API symbols.
• Builds and preloads a compatibility shim for SQLite C API symbols and formatting functions required by PHP's pdo_sqlite.
• Applies localized, workflow-only driver and test rewrites for known Turso compatibility differences.
• Runs focused smoke/probe coverage before PHPUnit.
• Runs each PHPUnit class in a fresh PHP process, aggregates the JUnit results, and fails on missing output, parse errors, test errors, or failures.

Turso source patches

The workflow applies these patches in order from .github/turso-patches/:

1. 01-stub-macro.py — return neutral values from unimplemented C API stubs instead of aborting PHP.
2. 02-column-functions-null-row.py — return SQLite-compatible null values when column accessors are called without a current row.
3. 03-create-function-v2-skip-old-destroy.py — avoid invoking stale UDF destroy callbacks when global function slots are reused.
4. 04-finalize-try-lock-on-gc-reentry.py — avoid finalize deadlocks during PHP GC re-entry from UDF callbacks.
5. 05-max-custom-funcs-32-to-64.py — expand the C binding's function bridge capacity for the driver's 44 UDFs.
6. 06-collation-mysql-aliases.py — map common MySQL collation names to compatible Turso built-ins.
7. 07-collate-direct-column-refs-only.py — limit implicit column collation inheritance to direct column references.
8. 08-create-trigger-preserve-original-sql.py — preserve the original CREATE TRIGGER SQL text in sqlite_master.
9. 09-hash-join-correlated-subquery.py — prevent incorrect hash joins in correlated query blocks.

The previous sqlite_sequence database-selection patch is no longer included because Turso fixed it upstream in 8f7d31f.

Refs: #204

Test plan

• All PR checks pass.
• All nine Turso source patches apply successfully.
• turso_sqlite3 builds successfully from the pinned source.
• The shared library exposes the expected sqlite3_* symbols.
• The pdo_sqlite smoke test and Turso compatibility probes pass.
• PHPUnit completes with 652/669 passing, 17 skipped, and zero errors or failures.

[JanJakes]

Closing this for now. We can reopen when needed. Turso DB is more behind SQLite than I thought. It's improving, but many patches are still needed. We can re-evaluate in the future.