fix(validation): Make unix_addr check useful (#1348)

[agentic-sanyam]

Hey folks,

This PR finally addresses #1348, where the unix_addr validation was, well, pretty much useless.

Turns out, net.ResolveUnixAddr for the "unix" network type in Go's standard library always succeeds (it just returns a UnixAddr struct with the provided name and network). This meant our isUnixAddrResolvable function always returned true, even for non-existent or invalid paths. Definitely not the behavior anyone would expect!

I've updated isUnixAddrResolvable to now leverage the existing isUnixDomainSocketExists function. This provides a much more robust check, ensuring the path actually exists and points to a valid Unix domain socket (or a Linux abstract socket).

Naturally, the TestUnixAddrValidation suite has been completely overhauled to reflect this new, stricter (and correct!) behavior. This includes:

• Adding a skip for Windows, as Unix domain socket existence checks aren't really a thing there.
• Dynamically creating a real Unix domain socket during the test to properly verify valid paths.
• Expanding test cases for empty strings and non-existent paths, which now correctly fail.

Now unix_addr actually does what users expect it to do! 🎉

Cheers!

Fixes #1348