fix: handle dead VMM and scan all urunc TAP devices during cleanup

[goyalpalak18]

Description

Fixed the issue where vmm.Stop() was returning an error if the process was already dead (like from a crash), which prevented network cleanup from running.

I updated killProcess in utils.go to treat ESRCH (process not found) as a success. If it's gone, it's gone, so we can proceed.

Also refactored network.Cleanup to actually scan for any tap.*_urunc interfaces instead of looking for a hardcoded string. This handles leftover devices much better.

Huge thanks to @sidneychang for the scanning logic in #407 — I integrated that here.

Related issues

Fixes #408
Integrates #407

How was this tested?

• make lint passes.
• Verified that killing the VMM process manually now properly triggers the network cleanup instead of failing.

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[cmainas]

Hello @goyalpalak18 ,

the changes look good. I have only left two small comments. Do not forget to fix the linting issues and rebase over main.

[goyalpalak18]

Thanks @cmainas ! Just pushed these updates and rebased over main. Let me know if everything looks good now.

[cmainas]

Thank you @goyalpalak18 for the changes. One thing I noticed is that if something fails during a cleanup of a single device then the function returns ignoring the rest. So it would be better to log the error but not return immediately but later at the end of the loop. Also, please rebase over main, so we can merge.