Add PHPUnit tests workflow for Doltlite

[JanJakes]

Summary

Runs the mysql-on-sqlite PHPUnit suite against Doltlite, a SQLite fork whose storage engine is a content-addressed prolly tree. The suite passes with the same counts as the local Doltlite verification run: 714 tests, 1,428,233 assertions, 15 skipped, 2 incomplete.

The workflow builds Doltlite from source, swaps the system libsqlite3 for it so PHP's pdo_sqlite transparently resolves against Doltlite, verifies the swap took effect, and then runs PHPUnit without any filters. The swap replaces the earlier LD_PRELOAD approach; LD_PRELOAD loses to pdo_sqlite's DT_NEEDED binding on libsqlite3.so.0.

Doltlite currently has four deviations from stock SQLite that break the driver. Each one is addressed by a narrow source-level patch applied before build, paired with a one-shot verify assertion in the workflow that fails fast if the patch stops applying or stops fixing the behavior:

1. Keep mysql-on-sqlite tables as rowid tables. Doltlite auto-converts ordinary composite/TEXT primary-key tables to WITHOUT ROWID, but the driver still relies on rowid access for table recreation, limited UPDATE/DELETE rewrites, on-update triggers, zero-column result statements, and metadata reads.

2. Keep merge scans aligned across committed tree rows and transaction-local mutmap entries. Without this, a deleted committed tree entry can still be emitted, and a mutmap-only row can be followed by a stale committed tree row outside the seek prefix.

3. Strip comments while canonicalizing schema SQL. Without this, rollback after a failed CHECK insert can collapse whitespace while preserving -- comments, leaving malformed CREATE TABLE SQL in sqlite_schema.

4. Use the current cursor key for auxiliary index deletes. Without this, deletes through non-key predicates can leave stale unique index entries visible inside the transaction.

Doltlite upstream already includes the previous eqSeen preservation and lossy-collation payload fixes. The workflow still verifies those behaviors so we catch regressions.

The patches are CI-only. Upstreaming them to Doltlite is a separate task.

Test plan

• PHPUnit Tests (Doltlite) runs green on this PR.
• Full PR check suite is green on the squashed branch.
• Local Docker verification against patched Doltlite: 714 tests, 1,428,233 assertions, 15 skipped, 2 incomplete.