fix(cursor): write CSI 6n query to TTY when stdout is redirected

[raphaelvigee]

Summary

Fixes #652.

cursor::position() on Unix wrote the ESC [ 6 n Device Status Report query to stdout. When stdout is piped to another program (e.g. prog | rev), the escape sequence went into the pipe instead of the terminal, so the terminal never responded and the call hung until the 2s timeout. The terminal's reply also corrupted the piped output.

Change

write_cursor_query picks the first available TTY for the query, in order:

1. stdout (preserved as default behavior when not redirected)
2. stderr
3. /dev/tty

The response is already read via tty_fd(), which falls back to /dev/tty when stdin is not a TTY, so the read side already worked — only the write side needed fixing.

rustix::termios::isatty is used for the TTY check (or libc::isatty under the libc feature). No new dependencies. MSRV 1.63 preserved (avoided std::io::IsTerminal, stable in 1.70).

Test plan

• cargo build (default features)
• cargo build --features libc
• cargo build --no-default-features --features events
• Manual: run a small binary that calls crossterm::cursor::position() with stdout piped to rev — confirm the call returns the cursor position instead of corrupting the pipe / timing out.
• Manual: same binary run normally in a terminal — confirm behavior unchanged.

[raphaelvigee]

I'm currently using the version 0.29 of the project, if this PR is accepted in principle i will update it to master