Improve error message for proxy connection failures

[hsenag]

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Note - this is only for me to play with, I opened it with Copilot Workspace without looking closely at what it did. I'm not expecting anyone else to review it in its current form.

Related to #84

Implements enhanced error handling for proxy connection failures across the HTTP library, specifically targeting scenarios where the proxy mentioned in http_proxy is down.

• Introduces a new error type ErrorProxyConnection in Network/Stream.hs to specifically handle proxy connection errors, improving error specificity and clarity for such issues.
• Updates error handling in Network/StreamSocket.hs to detect and report proxy connection failures, utilizing the new ErrorProxyConnection error type. This includes handling specific socket error codes related to proxy connection failures.
• Modifies Network/HTTP.hs to include the updated error handling mechanisms from Network/Stream.hs and Network/StreamSocket.hs, ensuring that proxy connection errors are correctly reported and logged, enhancing the overall robustness of the library in handling network-related errors.

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