Enhance error messages for connection failures (Fixes #6722)

[amritamishra01]

Summary

This PR improves the developer experience by providing more actionable and human-readable error messages for common connection failures, resolving #6722.

Currently, connection errors are often wrapped in a generic ConnectionError with a complex traceback that can be confusing for beginners. This change inspects the underlying exception to identify specific issues like DNS failures, refused connections, and unreachable networks.

Changes

• Modified HTTPAdapter.send in requests/adapters.py to inspect NewConnectionError and MaxRetryError.
• Added specific logic to detect and label:
  • DNS Failures (socket.gaierror): "Name resolution failed..."
  • Connection Refused (ConnectionRefusedError): "Connection refused by..."
  • Network Unreachable (OSError with errno 101/10051): "Network unreachable..."
• Preserved the original traceback using raise ... from e so advanced debugging context is not lost.

Verification

I verified these changes locally using a reproduction script that simulates:

1. A non-existent domain (DNS error).
2. A connection to a closed local port (Connection Refused).
3. A connection with a tiny timeout/unreachable network (Timeout/Unreachable).

All scenarios now output the enhanced, friendly error messages while maintaining the original exception chain.

[sigmavirus24]

The original issue was not sufficiently specified and hasn't responded to questions in two years. This is LLM slop without any test coverage, so we won't be accepting it