feat: process signaler

[wolfv]

Claude tried to fix our CTRL+C problems by adding a process signaler to deno task shell.
That should prevent:

• sending the signal twice
• not sending the signal

Blocked by: denoland/deno_task_shell#160

[baszalmstra]

before merging this I would like to better understand what was wrong with our current implementation.

[wolfv]

Our current implementation doesn't send CTRL+C when interactive:

        if signo == libc::SIGKILL
            || signo == libc::SIGSTOP
            || (signo == libc::SIGINT && is_interactive)  // Note: is_interactive check here
        {
            continue; // skip, can't listen to these
        }

I think we did that to prevent double-signaling the process on CTRL+C. However, that means we might not send it at all when sending kill to the parent process and it's in interactive state.

UV has a good comment about the problem: https://github.com/astral-sh/uv/blob/5f3d46c2413225aac68c86fa24be97c4c2c193e4/crates/uv/src/child.rs#L12-L24

[wolfv]

Basically this PR: e9b3d87 broke it again (but fixes double signaling). In reality we need deeper changes to make this work.