Several bugfixes and code improvements:
- Select pollen forecasts using the DWD timezone (thanks @SeoFood)
- Raise ConfigEntryNotReady when the initial fetch fails (thanks @mrueg)
- Parse the full DWD response before replacing the stored data (thanks @mrueg)
- Replace pytz with zoneinfo (thanks @mrueg)
- Use a DataUpdateCoordinator and fetch with aiohttp (thanks @mrueg)