housekeep(fastapi): rework aurweb.db session API

Changes:
-------
- Add aurweb.db.get_session()
    - Returns aurweb.db's global `session` instance
    - Provides us a way to change the implementation of the session
      instance without interrupting user code.
- Use aurweb.db.get_session() in session API methods
- Add docstrings to session API methods
- Refactor aurweb.db.delete
    - Normalize aurweb.db.delete to an alias of session.delete
- Refresh instances in places we depend on their non-PK columns
  being up to date.

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

aurweb/users/util.py

@@ -0,0 +1,19 @@
+from http import HTTPStatus
+
+from fastapi import HTTPException
+
+from aurweb import db
+from aurweb.models import User
+
+
+def get_user_by_name(username: str) -> User:
+    """
+    Query a user by its username.
+
+    :param username: User.Username
+    :return: User instance
+    """
+    user = db.query(User).filter(User.Username == username).first()
+    if not user:
+        raise HTTPException(status_code=int(HTTPStatus.NOT_FOUND))
+    return db.refresh(user)