refactor(wa-sqlite): initialize the extension after opening

[marcus-pousette]

Problem

TreeCRDT ran as a SQLite automatic extension, so OPFS file opening and asynchronous schema initialization shared one sqlite3_open_v2 retry budget. With wa-sqlite 1.1.1, both phases can pause for VFS work and exhaust that shared budget during startup.

Change

• Keep TreeCRDT statically linked, but initialize it explicitly after SQLite opens.
• Give schema initialization its own retry boundary, draining only concrete pending VFS work.
• Use the same open-then-initialize sequence in browser, worker, Node, and benchmark paths.
• Close database and VFS resources if explicit initialization fails.
• Pin wa-sqlite 1.1.1 / SQLite 3.53 at fork master commit 5bae8bd.

This isolates TreeCRDT initialization from sqlite3_open_v2. Generic failed-open handle cleanup is tracked separately in wa-sqlite #330 and does not block this fix.

Merge order

Merge this with a merge commit, then retarget #208 to main.