tests: fix resume mock session registration and RDRAM sizing

mock_netplay built a one-player session for a local handle of 1,
which the vendored ggrs fork rejects; register every handle (the
local player at player_number, dummy Remote PeerIds elsewhere).
The resume tests loaded saved states into fresh Device::new(false)
instances whose RDRAM backing store is empty, tripping
copy_from_slice in apply_savestate; pre-size the RDRAM like a real
emulated device, matching the saved session's RDRAM.

src/netplay.rs

@@ -1219,13 +1219,24 @@ mod tests {
         .build();
         let reliable_channel = socket.take_channel(1).unwrap();
 
-        let session = ggrs::SessionBuilder::<GgrsConfig>::new()
-            .with_num_players(1)
-            .unwrap()
-            .add_player(ggrs::PlayerType::Local, player_number)
-            .unwrap()
-            .start_p2p_session(TestSocket)
+        let mut builder = ggrs::SessionBuilder::<GgrsConfig>::new()
+            .with_num_players(player_number + 1)
             .unwrap();
+        // GGRS requires every handle to be registered: the local player at
+        // `player_number`, Remote placeholders (a dummy nil PeerId — the
+        // socket never sends to it) for the rest.
+        let dummy_peer: matchbox_socket::PeerId =
+            serde_json::from_str("\"00000000-0000-0000-0000-000000000000\"")
+                .expect("nil PeerId parses");
+        for handle in 0..=player_number {
+            let player_type = if handle == player_number {
+                ggrs::PlayerType::Local
+            } else {
+                ggrs::PlayerType::Remote(dummy_peer)
+            };
+            builder = builder.add_player(player_type, handle).unwrap();
+        }
+        let session = builder.start_p2p_session(TestSocket).unwrap();
 
         Netplay {
             disconnected: false,
@@ -1301,8 +1312,11 @@ mod tests {
 
         // Peer loads the embedded savestate into a fresh device (no disk),
         // exactly like resume_session_peer: load_from_memory ->
-        // load_savestate_from_data, then issue #5's frame reset.
+        // load_savestate_from_data, then issue #5's frame reset. The RDRAM
+        // backing store is pre-sized like a real emulated device, matching
+        // the saved session's RDRAM.
         let mut peer_device = crate::device::Device::new(false);
+        peer_device.rdram.mem.resize(0x800, 0);
         peer_device.netplay = Some(mock_netplay(1));
         apply_resume_state(&mut peer_device, &peer_save).expect("peer applies the state");
 
@@ -1363,7 +1377,10 @@ mod tests {
 
         // Fresh device stands in for the host's just-launched session; the
         // savestate was captured from a different Device instance above.
+        // RDRAM is pre-sized like a real emulated device so the saved
+        // session's RDRAM can be restored.
         let mut host_session = Device::new(false);
+        host_session.rdram.mem.resize(0x800, 0);
         host_session.ui.game_hash = "DEADBEEF-C01DF00D".to_string();
         host_session.netplay = Some(mock_netplay(0));
         host_session.netplay.as_mut().unwrap().state_path = Some(path.clone());