refactor: improve code formatting and readability in configuration and run files

- Simplified the assignment of `bot_username` in `config.py` for better clarity.
- Removed redundant import statement in `run.py` to streamline the code.
- Enhanced formatting in `group_duty_pin.py` and test files for improved readability and consistency.
- No functional changes were made; the focus was on code style and organization.

duty_teller/config.py

@@ -94,9 +94,7 @@ class Settings:
         )
         raw_host = (os.getenv("HTTP_HOST") or "127.0.0.1").strip()
         http_host = raw_host if raw_host else "127.0.0.1"
-        bot_username = (
-            (os.getenv("BOT_USERNAME", "") or "").strip().lstrip("@").lower()
-        )
+        bot_username = (os.getenv("BOT_USERNAME", "") or "").strip().lstrip("@").lower()
         return cls(
             bot_token=bot_token,
             database_url=os.getenv("DATABASE_URL", "sqlite:///data/duty_teller.db"),