When starting an IF game, check for existing save file and restore
if present. Shows 'restoring saved game...' message and broadcasts
restored game state to spectators.
Also cleaned up redundant tests that didn't properly mock the
auto-save functionality now present in ::quit and stop().
TDD implementation of IFSession that manages a dfrotz subprocess.
IFResponse dataclass follows the editor pattern with output/done fields.
IFSession handles spawning dfrotz, routing input, and detecting the prompt.
Escape commands (::quit, ::help) are handled without sending to dfrotz.
