Replaces the async _do_restore() (called after thread launch) with a
synchronous _try_restore() called before the thread starts. This
eliminates the race condition where restore mutates z-machine state
while the interpreter thread is running.
The restore prefix message is now part of start()'s return value
instead of being sent separately in play.py.
Unit tests for MUD UI components (screen, input stream, filesystem)
and integration tests with real zork1.z3 (session lifecycle, escape
commands, save/restore round-trip, state inspection).
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().
