setPassthrough method
Enables or disables raw passthrough. While on, bytes from the input are
forwarded verbatim to onRaw (bypassing line editing); the local edit
buffer and any partial escape/UTF-8 state are reset on each transition.
Implementation
void setPassthrough(bool on) {
if (_passthrough == on) return;
_passthrough = on;
_state = _ParseState.normal;
_csiParams = '';
_utf8.clear();
_utf8Need = 0;
_buffer.clear();
_cursor = 0;
}