Fix system binary sensors not updating fixes #736

[andyblac]

Summary

Fixes #736.

Wiser system binary sensors now refresh their state when new coordinator data is received.

Previously, SystemBinarySensor._handle_coordinator_update() returned a generated HeatHub name string. Home Assistant ignored this return value, leaving the entities at the state captured during initial setup.

Changes

• Read the latest system property during each coordinator update.
• Update the entity’s internal state.
• Write the updated state to Home Assistant.
• Use an unknown state when the property is temporarily absent.
• Retain the existing historical unique-ID handling.

Affected entities

• Summer discomfort prevention
• Summer comfort available
• PCM device limit reached

Validation

• Confirmed coordinator updates refresh the entity state.
• Confirmed the updated state is written to Home Assistant.
• Confirmed a temporarily missing property produces an unknown state.
• Added focused regression tests for both cases.