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_initdb.py

@@ -1,3 +1,5 @@
+import pytest
+
 import aurweb.config
 import aurweb.db
 import aurweb.initdb
@@ -5,6 +7,11 @@ import aurweb.initdb
 from aurweb.models.account_type import AccountType
 
 
+@pytest.fixture(autouse=True)
+def setup(db_test):
+    return
+
+
 class Args:
     use_alembic = True
     verbose = True
@@ -15,6 +22,8 @@ def test_run():
     aurweb.db.kill_engine()
     metadata.drop_all(aurweb.db.get_engine())
     aurweb.initdb.run(Args())
+
+    # Check that constant table rows got added via initdb.
     record = aurweb.db.query(AccountType,
                              AccountType.AccountType == "User").first()
     assert record is not None