Fix bugs and align with HA standards

[peternijssen]

While working on a DHL component with Claude, I've requested Claude to also review this repository. I believe it found valid improvements and fixes. Just waiting for a package to arrive in PostNL to see if everything still functions as expected.

Fix bugs and align with HA standards

Bug fixes

• AttributeError on coordinator update — PostNLCoordinator referenced self.config_entry without ever assigning it. The constructor now accepts and stores the ConfigEntry.
• Wrong base class — PostNLDelivery inherited from Entity instead of SensorEntity, preventing correct registration as a sensor platform entity.
• Crash on None coordinator data — handle_coordinator_data accessed coordinator.data['receiver'] directly without guarding against None, which is always the case when called from init before the first refresh. Now uses .get() with a fallback and an early return.
  *AttributeError on ClientError.status — only ClientResponseError has a status attribute, not the parent ClientError. Added an isinstance check before accessing .status.

Security

• OAuth access token removed from logs — auth.access_token was logged at debug level, exposing a live token to anyone with HA log access.

HA standards

• SensorStateClass.MEASUREMENT added to both sensors, enabling long-term statistics in HA.
• DeviceEntryType.SERVICE and configuration_url added to DeviceInfo.
• state and unit_of_measurement properties replaced with native_value and _attr_native_unit_of_measurement / _attr_icon class variables (modern HA pattern since 2022.5).
• requests added to manifest.json requirements.

Minor

*async_setup_entry return type corrected from -> True to -> bool.

• Log message in async_unload_entry corrected from "Reloading" to "Unloading".