stty: fix output redirection

[willshuttleworth]

Fix related to this issue. I have removed the Device enum that had a variant for a file and for stdout. Instead, just using a file passed with --file flag or /dev/tty by default. Output redirection (redirecting to file or pipe) now works.

In terms of testing, the same issues exist with other stty testing as cargo test doesn't run in a tty. I have added tests in a related PR, but these tests are limited to inputs that should fail.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[willshuttleworth]

Instead of defaulting to /dev/tty with no fallback, now I'm trying /dev/tty first then falling back to stdout

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/stdbuf (passes in this run but fails in the 'main' branch)

[cakebaker]

Thanks for your PR!