fix: remove backoff in case of failures

[lhw]

Weathercloud seems unreliable. And without an option to re-enable the sending this is just annoying.

Also its at most one request per minute. So whatever

[Copilot]

Pull request overview

This pull request removes the proxy failure tracking and automatic backoff mechanism that was previously disabling weather service proxies after repeated failures. The change is motivated by Weathercloud being unreliable and the fact that weather stations send updates infrequently (at most once per minute), making permanent disabling of forwarding problematic when there's no way to re-enable it without reconfiguration.

Changes:

• Removed failure tracking data structures (proxy_failure_counts and disabled_proxy_sinks)
• Simplified error handling to log failures without counting or disabling proxies
• Improved session.closed handling to allow retries on subsequent requests rather than permanent disabling