fix: catch kqueue EINVAL selector error on uv-managed macOS Python

[henrytran1803]

Summary

• On macOS with uv-managed cPython, the kqueue selector fails to register stdin (fd 0) with OSError: [Errno 22] Invalid argument. The existing error handlers only caught errno.EIO and string-matched "is not registered" / "Bad file descriptor", causing an unhandled crash.

Changes

1. Selector probe — Before launching prompt_toolkit, actively tries to register fd 0 with selectors.DefaultSelector(). Catches the failure early with a user-friendly message instead of a traceback.
2. Async exception handler — Added errno.EINVAL alongside errno.EIO so kqueue EINVAL errors are suppressed in the event loop handler.
3. app.run() exception handler — Added errno.EINVAL to the errno check and "Invalid argument" to the string match.

Test plan

• Reproduced the crash on macOS with uv-managed cPython 3.11 (/Users/henrytran/.local/share/uv/python/cpython-3.11.15-macos-aarch64-none/)
• Verified the fix shows a clean error message instead of a traceback
• Existing tests for stdin/stdout error handling remain unaffected

[alt-glitch]

Likely duplicate of #11253, #8796, #13251, #11866, #9996 — same kqueue EINVAL on macOS stdin selector registration. Multiple competing PRs already exist for #6393.

[alt-glitch]

Likely duplicate of #11253, #8796, #13251, #11866, #9996 — same kqueue EINVAL on macOS stdin selector registration.

[teknium1]

Closing — superseded by #26077 (merged as commit d3d5916), which preventively probes kqueue at startup and falls back to SelectSelector when fd 0 cannot be registered. The widened except-clause matching EINVAL / EBADF / 'Invalid argument' — which most PRs in this cluster including yours added — is also included.

Thanks for the fix; closing as duplicate of the merged work.