Opaque container for a saved termios(3) state.

Returned by Linx.Tty.open_controlling_raw/0 and consumed by Linx.Tty.restore_and_close/2. The wrapped binary is a verbatim copy of the kernel's struct termios — its bytes are not part of the public API. Inspecting or modifying them from Elixir is a bug; always hand the struct back to the matching restore function.

Wrapping it in a struct (rather than handing back a raw binary) makes the type visible at call sites and prevents accidentally passing the wrong binary as a saved termios.