[FastAPI] Refactor db modifications

For SQLAlchemy to automatically understand updates from the
external world, it must use an `autocommit=True` in its session.

This change breaks how we were using commit previously, as
`autocommit=True` causes SQLAlchemy to commit when a
SessionTransaction context hits __exit__.

So, a refactoring was required of our tests: All usage of
any `db.{create,delete}` must be called **within** a
SessionTransaction context, created via new `db.begin()`.

From this point forward, we're going to require:

```
with db.begin():
    db.create(...)
    db.delete(...)
    db.session.delete(object)
```

With this, we now get external DB modifications automatically
without reloading or restarting the FastAPI server, which we
absolutely need for production.

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

test/test_api_rate_limit.py

@@ -2,6 +2,7 @@ import pytest
 
 from sqlalchemy.exc import IntegrityError
 
+from aurweb import db
 from aurweb.db import create
 from aurweb.models.api_rate_limit import ApiRateLimit
 from aurweb.testing import setup_test_db
@@ -13,26 +14,28 @@ def setup():
 
 
 def test_api_rate_key_creation():
-    rate = create(ApiRateLimit, IP="127.0.0.1", Requests=10, WindowStart=1)
+    with db.begin():
+        rate = create(ApiRateLimit, IP="127.0.0.1", Requests=10, WindowStart=1)
     assert rate.IP == "127.0.0.1"
     assert rate.Requests == 10
     assert rate.WindowStart == 1
 
 
 def test_api_rate_key_ip_default():
-    api_rate_limit = create(ApiRateLimit, Requests=10, WindowStart=1)
+    with db.begin():
+        api_rate_limit = create(ApiRateLimit, Requests=10, WindowStart=1)
     assert api_rate_limit.IP == str()
 
 
 def test_api_rate_key_null_requests_raises_exception():
-    from aurweb.db import session
     with pytest.raises(IntegrityError):
-        create(ApiRateLimit, IP="127.0.0.1", WindowStart=1)
-    session.rollback()
+        with db.begin():
+            create(ApiRateLimit, IP="127.0.0.1", WindowStart=1)
+    db.rollback()
 
 
 def test_api_rate_key_null_window_start_raises_exception():
-    from aurweb.db import session
     with pytest.raises(IntegrityError):
-        create(ApiRateLimit, IP="127.0.0.1", Requests=1)
-    session.rollback()
+        with db.begin():
+            create(ApiRateLimit, IP="127.0.0.1", Requests=1)
+    db.rollback()