change(aurweb): add parallel tests and improve aurweb.db

This change utilizes pytest-xdist to perform a multiproc test
run and reworks aurweb.db's code. We no longer use a global
engine, session or Session, but we now use a memo of engines
and sessions as they are requested, based on the PYTEST_CURRENT_TEST
environment variable, which is available during testing.

Additionally, this change strips several SQLite components
out of the Python code-base.

SQLite is still compatible with PHP and sharness tests, but
not with our FastAPI implementation.

More changes:
------------
- Remove use of aurweb.db.session global in other code.
- Use new aurweb.db.name() dynamic db name function in env.py.
- Added 'addopts' to pytest.ini which utilizes multiprocessing.
    - Highly recommended to leave this be or modify `-n auto` to
      `-n {cpu_threads}` where cpu_threads is at least 2.

Signed-off-by: Kevin Morris <kevr@0cost.org>

aurweb/routers/auth.py

@@ -6,7 +6,7 @@ from fastapi.responses import HTMLResponse, RedirectResponse
 
 import aurweb.config
 
-from aurweb import cookies
+from aurweb import cookies, db
 from aurweb.auth import auth_required
 from aurweb.l10n import get_translator_for_request
 from aurweb.models import User
@@ -45,9 +45,7 @@ async def login_post(request: Request,
         raise HTTPException(status_code=HTTPStatus.BAD_REQUEST,
                             detail=_("Bad Referer header."))
 
-    from aurweb.db import session
-
-    user = session.query(User).filter(User.Username == user).first()
+    user = db.query(User).filter(User.Username == user).first()
     if not user:
         return await login_template(request, next,
                                     errors=["Bad username or password."])