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>

test/test_cache.py

@@ -3,14 +3,11 @@ import pytest
 from aurweb import cache, db
 from aurweb.models.account_type import USER_ID
 from aurweb.models.user import User
-from aurweb.testing import setup_test_db
 
 
 @pytest.fixture(autouse=True)
-def setup():
-    setup_test_db(
-        User.__tablename__
-    )
+def setup(db_test):
+    return
 
 
 class StubRedis: