refactor: improve code readability and structure in various components

- Refactored the `mini_app_short_name` assignment in `config.py` for better clarity.
- Enhanced the `app_config_js` function in `app.py` to improve formatting of the JavaScript response body.
- Added per-chat locks in `group_duty_pin.py` to prevent concurrent refreshes, improving message handling.
- Updated `_schedule_next_update` to include optional jitter for scheduling, enhancing performance during high-load scenarios.
- Cleaned up test files by removing unused imports and improving test descriptions for clarity.

duty_teller/config.py

@@ -172,7 +172,9 @@ class Settings:
             database_url=database_url,
             bot_username=bot_username,
             mini_app_base_url=os.getenv("MINI_APP_BASE_URL", "").rstrip("/"),
-            mini_app_short_name=(os.getenv("MINI_APP_SHORT_NAME", "") or "").strip().strip("/"),
+            mini_app_short_name=(os.getenv("MINI_APP_SHORT_NAME", "") or "")
+            .strip()
+            .strip("/"),
             http_host=http_host,
             http_port=http_port,
             allowed_usernames=allowed,