network: general fixes for failure states

[edsiper]

fixes: https://github.com/fluent/fluent-bit/issues/10458

In addition, other fixes are part of this PR for async DNS resolution (remove stale fd from the event loop), extra validation of socket status for a synchronous network connection and the busy_flag management in the upstream interface.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.