fix(tests): remove stale Windows TTY assumptions

[coderbants]

Closes #5.

Summary

• remove the stale Windows test that still required raw-mode operations to be infallible no-ops
• retain tests/windows_tty.rs as the native Windows lifecycle and console-availability proof
• remove the duplicate Unix crate gate from the already target-gated PTY test
• update the upstream mapping to name the surviving Windows regression

This is the recorded non-material test-only descendant requested after PR #7 merged. It does not change the public API or production implementation.

Verification

• native Windows windows_tty regression: 3 passed, 0 failed at exact head ba2f03e0fb513a7b3edb0c48dd4c109b725ab410
• cargo fmt --manifest-path Cargo.toml -p rusty-bubbletea -- --check: passed
• git diff --check origin/dev..HEAD: passed