Add vehicle timetable get/set support

Timetables have no GameScript API surface, so this implements real
DoCommands over the game port (ClientCommand/ServerCommand) instead of
the Admin GameScript relay used for list_vehicles(): change_timetable(),
autofill_timetable(), set_timetable_start(), and set_vehicle_on_time()
send commands, while get_vehicle_timetable() reconstructs state purely
by observing ServerCommand broadcasts, since no query command exists.

Includes the custom varuint wire codec these commands require, a full
usage guide (docs/TIMETABLES.md), and a worked demo in main.py.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_logic.py

@@ -118,11 +118,10 @@ async def test_fallback_handlers():
     await client.receive_ServerConfigurationUpdate(None)
     await client.receive_ServerClientInfo(None)
     await client.receive_ServerExternalChat(None)
-    await client.receive_ServerCommand(None)
     await client.receive_ClientAck(None)
     await client.receive_ClientIdentify(None)
     await client.receive_ServerCompanyUpdate(None)
-    
+
     client.joined.set()
     await client.join_company(0)
 
@@ -224,7 +223,6 @@ async def test_unit_client_noop_callbacks(server_config):
     await client.receive_ServerMapData(None)
     await client.receive_ServerConfigurationUpdate(None)
     await client.receive_ServerExternalChat(None)
-    await client.receive_ServerCommand(None)
     await client.receive_ServerFull(None)
     await client.receive_ServerBanned(None)
     await client.receive_ClientAck(None)