Let the SQLite busy timeout be set, as DATABASE_CONNECTION_TIMEOUT sets it in Drivine for TypeScript #463

Drivine for TypeScript lets you set how long a SQLite connection waits for the file's write lock, with DATABASE_CONNECTION_TIMEOUT. drivine-python fixes it at 30 seconds, and its connection builder can't set it.

Fix: read the same setting, from the environment variable and the builder, with 30 seconds as the default. Document it in docs/02-connecting.md's SQLite section.

Found while moving the README's SQLite section into the docs (#460). This is outside the compiler, so it's a normal fix.