[host][darwin]: fix utmpx database parsing

[uubulb]

Close #1989

Fixed the parsing logic in UsersWithContext() to align with the current implementation of getutxent(), which uses the compatibility struct utmpx32 to read the utmpx database file /var/run/utmpx.

Since utmpx32 is not available in the system headers, the struct definition must be manually copied from the Darwin Libc source.

[shirou]

Thank you for your swift PR. This PR changes previously exported types like Utmpx to unexported. This might be a breaking change, but I think it's acceptable since these types were likely not intended to be part of the public API.

I don't have a Mac machine, so I cannot verify this PR works correctly, but it looks good to me.

@nook24, could you verify this PR solves your issue?

[nook24]

I successfully tested this on an M4 and Intel Mac.

My results:

macOS 26.2 - arm64

User:  macbert
Terminal:  ttys000
Host:
Started:  1768375108

macOS 15.6.1 - Intel

User:  nook24
Terminal:  ttys005
Host:  
Started:  1758904387

Linux (for comparison)

User:  herbert
Terminal:  pts/1
Host:
Started:  1768374935

This was my testing code: https://github.com/nook24/gopsutil-user-test

Thanks for this quick fix! Awesome

[shirou]

Thank you for confirming this, @nook24, and many thanks to @uubulb for the help!