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]>

tests/test_admin.py

@@ -388,6 +388,40 @@ async def test_admin_get_station_cargo_error_response():
         await task
     assert client._gs_futures == {}
 
+@pytest.mark.asyncio
+async def test_admin_list_cargo_request_and_response():
+    client = OpenTTDAdminClient("127.0.0.1", port=3977, admin_name="TestAdmin")
+    proto = MockProtocol()
+    client._protocol = proto
+    client._transport = MockTransport()
+
+    task = asyncio.ensure_future(client.list_cargo())
+    await asyncio.sleep(0)  # let the task send the request
+
+    # First use auto-subscribes to Gamescript updates, then sends the query.
+    assert len(proto.sent) == 2
+    assert proto.sent[0][2] == PacketAdminType.AdminUpdateFrequency
+    assert decode_gamescript_payload(proto.sent[1]) == {
+        "command": "list_cargo", "request_id": 1,
+    }
+
+    response = {"command": "list_cargo", "request_id": 1,
+                "cargo": [{"cargo_id": 0, "label": "PASS", "freight": 0},
+                          {"cargo_id": 1, "label": "COAL", "freight": 1}]}
+    await client.receive_ServerGamescript(None, data=response)
+    assert await task == response
+    assert client._gs_futures == {}
+
+@pytest.mark.asyncio
+async def test_admin_list_cargo_timeout():
+    client = OpenTTDAdminClient("127.0.0.1", port=3977, admin_name="TestAdmin")
+    client._protocol = MockProtocol()
+    client._transport = MockTransport()
+
+    with pytest.raises(asyncio.TimeoutError):
+        await client.list_cargo(timeout=0.05)
+    assert client._gs_futures == {}
+
 @pytest.mark.asyncio
 async def test_admin_get_dispatch_request_and_response():
     client = OpenTTDAdminClient("127.0.0.1", port=3977, admin_name="TestAdmin")