gh-108083: Don't ignore exceptions in sqlite3.Connection.__init__() and .close()...

gh-108083: Don't ignore exceptions in sqlite3.Connection.__init__() and .close() (#108084)

- Add explanatory comments
- Add return value to connection_close() for propagating errors
- Always check the return value of connection_exec_stmt()
- Assert pre/post state in remove_callbacks()
- Don't log unraisable exceptions in case of interpreter shutdown
- Make sure we're not initialized if reinit fails
- Try to close the database even if ROLLBACK fails

Co-authored-by: Victor Stinner <vstinner@python.org>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>