Improve serial handling and local key error reporting

[j-k-olofsson]

This PR improves robustness and diagnostics for local Alsavo/Zealux connections.

Changes:

• Strip non-digit characters from the serial number before using it for protocol authentication.
• Detect empty/reset query responses and raise a clearer error suggesting that the local key/password should be checked.
• Increase UDP receive timeout from 5 to 20 seconds.
• Increase Home Assistant coordinator timeout from 10 to 30 seconds.

Background:
While troubleshooting a local pool heat pump setup, the integration could authenticate far enough to receive a handshake but then received reset/empty query responses when the local key was wrong. This resulted in unavailable entities without a useful diagnostic message.

Tested:

• Verified with a local test Home Assistant container.
• Verified successful status/config updates after correcting the local key.
• Verified Python files compile with py_compile.