fix: swallow resize() errors after PTY exit on Windows and Unix

[euxaristia]

Summary

• Silently ignore resize() calls after the PTY process has already exited instead of throwing 'Cannot resize a pty that has already exited' (Windows)
• Catch EBADF errors on resize() when the PTY file descriptor is already closed and silently return instead of crashing (Unix)
• Prevents crashes on both platforms when a resize is triggered after process exit (e.g. during terminal cleanup)

Fixes #827

Details

Windows: The native conpty _exitCode guard previously threw an error, which could crash the host process if the caller didn't wrap resize() in a try/catch. This is a race condition that's more likely to surface on Node.js v22 due to timing changes in its stream/event loop internals.

Unix: pty.resize() throws 'ioctl(2) failed, EBADF' when the PTY file descriptor has already been closed before a resize event fires. The fix catches EBADF by both error code and message and silently returns.

Test plan

• Reproduce crash from Windows crash on Node.js v22 – "Cannot resize a pty that has already exited" #827 on Windows + Node.js v22, confirm it no longer throws after this change
• Trigger a resize after PTY exit on Unix, confirm EBADF is no longer thrown
• Verify normal resize still works when PTY is active on both platforms

[euxaristia]

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