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>

README.md

@@ -10,6 +10,7 @@ A high-performance, Object-Oriented Python client for OpenTTD servers, specifica
 - **State Management:** Handles the full join sequence including Map download and synchronization.
 - **Comprehensive Testing:** Robustly tested with unit, logic, and E2E tests (including 100% coverage for unit/logic tests).
 - **Vehicle Listing:** Query vehicle data via the Admin GameScript channel with `list_vehicles()`.
+- **Vehicle Timetables:** Read and modify a vehicle's timetable (`change_timetable()`, `autofill_timetable()`, `set_timetable_start()`, `set_vehicle_on_time()`, `get_vehicle_timetable()`) via real game-protocol commands.
 
 ## 🛠 Setup
 
@@ -73,4 +74,5 @@ For detailed instructions on E2E testing and coverage reports, see the [Testing
 ## 📜 Documentation
 - [Architecture & Design](docs/ARCHITECTURE.md)
 - [Protocol Internals (PAKE/Encryption)](docs/PROTOCOL.md)
+- [Vehicle Timetables Usage Guide](docs/TIMETABLES.md)
 - [Contributor Guide](docs/CONTRIBUTING.md)