[quotentiroler]

Refs #2970

executescript() does not open a transaction, so the ~1,440 INSERTs in TABLES each committed separately.

Wrapping the script in BEGIN; / COMMIT; takes populate_fixture_database() from 11,453 ms to 19 ms here (single process, best of three, Windows 11 / Python 3.14), producing an identical database: a sha256 over every table's full contents matches.

This runs on every make_app_client(), so it is the bulk of the suite's setup cost. pytest tests/test_html.py tests/test_queries.py tests/test_stored_queries.py went from 470.6s to 28.7s with the same pass/fail counts.

[quotentiroler]

@simonw CI on this PR never ran: every fork PR opened Sep 30 to Oct 1 failed instantly with zero jobs ("workflow file issue"), the same for #2973 and several others. I've rebased onto current main to trigger it again.

The speedup holds on Linux too. In python:3.13-slim, building the fixture database takes a median of 21.8 s on main and 65 ms with this change, with identical contents. make_app_client rebuilds that file on every call, so it adds up: pytest -n auto tests/test_fixtures.py tests/test_html.py takes 398 s on main and 12 s on this branch, both with 150 passed, 1 xpassed. (Docker on WSL2, whose disk syncs are slower than a GitHub runner's, so expect a smaller but still large gain in CI.)