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/run.py

@@ -11,6 +11,7 @@ from telegram.ext import ApplicationBuilder
 from duty_teller import config
 from duty_teller.config import require_bot_token
 from duty_teller.handlers import group_duty_pin, register_handlers
+from duty_teller.utils.http_client import safe_urlopen
 
 
 async def _resolve_bot_username(application) -> None:
@@ -19,7 +20,7 @@ async def _resolve_bot_username(application) -> None:
         me = await application.bot.get_me()
         config.BOT_USERNAME = (me.username or "").lower()
         logger.info("Resolved BOT_USERNAME from API: %s", config.BOT_USERNAME)
-from duty_teller.utils.http_client import safe_urlopen
+
 
 logging.basicConfig(
     format="%(asctime)s - %(name)s - %(levelname)s - %(message)s",