Add list_cargo() to the admin client

The station queries and the cargo events name a cargo only by a bare
numeric id -- get_station()'s and get_station_cargo()'s cargo_id, the
cargo_waiting events, the per-cargo load on vehicle events. Those ids
index the cargo table the loaded NewGRFs build for the running game, so
the same id is coal in one save and grain in another and callers had no
way to resolve them. The AdminBridge GameScript has answered a list_cargo
command all along; no method on OpenTTDAdminClient sent it. This adds the
missing half, so no GameScript change is needed for it to work.

It goes through _gs_query() like get_station(), inheriting the request_id
correlation and the Gamescript auto-subscribe, with one difference worth
knowing: the GS handler defines no error reply for this command, so unlike
the other queries it can time out but can never raise ValueError.

The reply lists cargo in GSCargoList order rather than by id -- against
the dev server the ids come back 10 down to 0 -- so the docstring and
PROTOCOL.md both warn to index the list by cargo_id and not by position.

Also teaches the main_admin.py demo to resolve the labels before printing
a station's cargo, which is what the bare ids in its output were asking
for all along.

Co-Authored-By: Claude <[email protected]>

README.md

@@ -17,6 +17,7 @@ A high-performance, Object-Oriented Python client for OpenTTD servers, specifica
 - **Station Listing:** Enumerate stations via the Admin GameScript channel with `list_stations()`.
 - **Station Cargo Snapshots:** `OpenTTDAdminClient.get_station()` returns a station's live per-cargo state from the running game — both the **real-time** amount waiting and the **planned** flow through the cargodist link graph — over the AdminBridge GS (stock GameScript API, no server patch needed).
 - **Cargo Flow Breakdown:** `OpenTTDAdminClient.get_station_cargo()` breaks one cargo type down by **source station** and **next hop** (routing destination) for both waiting (real-time) and planned amounts, with optional `from_station`/`via_station` filters.
+- **Cargo Table:** `OpenTTDAdminClient.list_cargo()` names the bare `cargo_id`s the station queries and cargo events return — every cargo type in the running game with its label (`PASS`, `COAL`, …) and freight flag, read live so NewGRF-specific ids resolve correctly.
 - **Game Events:** react to the game instead of polling it — `subscribe_events()` streams events over the AdminBridge GS as they happen: a vehicle reaching or leaving a stop (`vehicle_arrive`/`vehicle_depart`, with dwell time and cargo aboard), a station's waiting cargo changing (`cargo_waiting`), plus crashes, industries opening/closing, towns, companies and subsidies. Consume them with `await wait_for_event()` or an `on_event` callback; filter by kind, company, vehicle, station or cargo.
 
 ## 🛠 Setup