Added Processes to IONative

[rahulrangers]

Implemented ProcessBuilder-based process spawning for Scala Native using posix_spawn, with support for stdin, stdout, and stderr piping. Integrated pidfd_open and fileDescriptorPoller to asynchronously and non-blockingly wait for process termination. Falls back to waitpid when pidfd_open is unavailable.

[rahulrangers]

@armanbilge can you please review this PR

[armanbilge]

Thanks, nice work! A few quick thoughts:

1. Let's try to get CI green. The native bindings you introduced may need @nowarn annotations (there should be other examples in the codebase).
2. I think we can unguard some ProcessSuite tests, at least on Linux.
3. We may want to keep the java.lang.Process implementation in shared sources, and use it as a fallback on Native for non Linux/macOS (i.e. Windows).

[antoniojimeneznieto]

I checked the timeout exception in the env inheritance test. I think the issue comes in how the envMap/envp is being constructed. Interestingly, adding a dummy variable when the Map is empty seems to solve the problem.

[rahulrangers]

@antoniojimeneznieto Yep, I tried using dummy variable, and it actually resolved the issue.
However, using dummy variable doesn't result in countEnv(false) == 0 as it does on the JVM platform. Instead, we get countEnv(true) > countEnv(false), which still causes the test to pass.
So I’m unsure if this is the correct fix, since the behavior isn’t exactly the same.

Also, I’m not fully understanding why the EOF signal isn’t being triggered in readFd, which is preventing the loop from exiting. Currently, both test cases failing in CI is due to this issue.

[antoniojimeneznieto]

Yes! this isn't a fix, since it may introduce other issues or conflicts. It was more of a remark than a proper solution, sorry for the confusion.

[rahulrangers]

@armanbilge @antoniojimeneznieto I have found the issue, The epollSystem was not including EPOLLHUP, which is necessary to detect when the pipe has been closed by a process. This is the reason why the testcases are failing.
I have made a PR to handle EPOLLHUP typelevel/cats-effect#4422

[rahulrangers]

@armanbilge can you please review this PR

[armanbilge]

I am sorry it took me so long to give this the review it deserves! Overall this looks very good and so happy to seem so many tests enabled in the test suite :) great job with that

I do have a quite a bit of feedback but it is mostly polish. Also, a general advice is to use more of the helpers like guard_ and errnoToThrowable in NativeUtil.

[armanbilge]

Suggested change

	object SyscallBindings {
	private object syssyscall {

[armanbilge]

We can move the bindings to fs2/io/native/src/main/scala/fs2/io/internal

[armanbilge]

Suggested change

	def forAsync[F[_]: LiftIO](implicit F: Async[F]): Processes[F] =
	def forLiftIO[F[_]: LiftIO](implicit F: Async[F]): Processes[F] =

[armanbilge]

What is the purpose of this else? Since it doesn't seem to use the status.

[rahulrangers]

we are having else to remove the zombie process from the kernel space as given in this:
A child that terminates, but has not been waited for becomes a
"zombie".
https://man7.org/linux/man-pages/man2/waitpid.2.html