[TASK] Run the functional tests on SQLite

[benjaminkott]

Description

The functional tests run on SQLite. The mysql:8.0 service is gone
from the CI and the typo3Database* variables are gone from the DDEV
container.

The driver is declared in Build/phpunit-functional.xml, not in the CI
job, so a local checkout and the CI run the suite the same way and
neither carries database settings.

The service was started in all eight matrix jobs while only the two
8.5 ones actually run the functional tests — every other job paid for
a database it never touched. SQLite needs no service at all.

Nothing but the testing framework ever read the four typo3Database*
variables: the development instance takes its connection from the DDEV
generated config/system/additional.php, which points at db/db,
not at the t3func/root those variables described. Running the suite
against MySQL is still possible, it just means setting
typo3DatabaseDriver and the connection variables yourself; AGENTS.md
says so.

It is also faster. Measured locally on the full suite (72 tests, PHP
8.5, MySQL 8.0 in a neighbouring container):

Driver	Time
MySQL 8.0	154 s
pdo_sqlite	92 s

Same 72 tests, same 378 assertions on both. The gain is setup, not
queries: with SQLite the testing framework builds the schema once per
test case and copies the empty database file for every following test
instead of truncating tables. In the CI the functional jobs went from
5m12s and 6m05s to 3m32s and 4m25s, and the six jobs that run no
functional tests from around a minute to half of that.

The trade off is that the CI no longer exercises MySQL. The package
reaches the database through TCA, QueryBuilder and DataHandler; after
#1661 there is no hand written SQL left in the tests.

Type of change

• Bugfix
• Task
• Feature
• Documentation

Related issues

Builds on #1661, which removed the last MySQL specific SQL from the
test suite.

How to validate

1. The CI run on this pull request — the functional jobs are green
   without a database service.
2. Nothing reaches MySQL any more, with the DDEV database deliberately
   out of reach:
   ddev exec bash -c 'typo3DatabaseHost=doesnotexist .build/bin/phpunit -c Build/phpunit-functional.xml'
   — 72 tests, 378 assertions, green.
3. And with the variables gone rather than wrong:
   ddev exec bash -c 'unset typo3DatabaseHost typo3DatabaseName typo3DatabaseUsername typo3DatabasePassword; .build/bin/phpunit -c Build/phpunit-functional.xml'
   — same result.
4. The override still works: run 2 with typo3DatabaseDriver=mysqli
   prepended fails on the unreachable host.

A ddev restart is needed for the container to drop the variables.

AI assistance

• Agent and version: Claude Code, VS Code extension
• Model and effort/reasoning level: Claude Opus 5 (1M context), default
  effort
• Share written by the agent: the whole change and this description
• Reviewed and understood before pushing: not yet — opened on request,
  review pending

Checklist

• Targets master
• Commits are signed off (git commit -s)
• Commit subjects follow [BUGFIX|TASK|FEATURE] Subject
• composer cgl leaves the code unchanged — no PHP touched
• composer phpstan passes — no PHP touched
• composer test passes
• A bugfix comes with a test that fails without it — not
  applicable
• Holds on every TYPO3 and PHP version declared in composer.json
  — the CI matrix itself is unchanged
• Assets rebuilt — not applicable
• Documentation updated — AGENTS.md; Documentation/ says
  nothing about the test database