fix(parser): parse CSI Z as shift+tab

[nowaymyname27]

Summary

• add CSI Z handling in Parser.parseCsi to emit Shift+Tab (Key.tab with mods.shift = true)
• add parser test coverage for \x1b[Z (parse: xterm shift+tab)
• closes the gap reported for macOS terminals emitting CSI Z for Shift+Tab

Testing

• zig build test

[nowaymyname27]

Thanks for maintaining vaxis. I recently started using it in a personal project and wanted to contribute a small fix. This PR addresses #266 by handling CSI Z as Shift+Tab and adds parser test coverage. Happy to adjust anything if you’d prefer a different approach.

[rockorager]

Thanks!