Handle keepalive packets in server loading state

[MhaWay]

Summary

Handle Client_KeepAlive packets while the connection is in ServerLoading.

Fixes #861.

What changed

• add keepalive handling to ServerLoadingState
• update latency / behind / simulation tracking in the same way as ServerPlayingState
• add a regression test that sends a keepalive while the server is blocked waiting for join point completion

Why this fixes the issue

Previously, a reconnecting client could continue sending keepalive packets while the server was still in ServerLoading, and the server would log them as unhandled packets.

After this change, the loading state accepts those packets normally, which removes the server log spam and keeps connection bookkeeping coherent during reconnect/loading.

Validation

• dotnet test Source/Tests/Tests.csproj --filter "FullyQualifiedName~LoadingStateHandlesKeepAliveWhileWaitingForJoinPoint"
• dotnet build Source/Server/Server.csproj -c Release

[Copilot]

Pull request overview

This PR updates the server’s ServerLoading connection state to accept and process Client_KeepAlive packets (matching ServerPlaying behavior) to prevent “unhandled packet” log spam during reconnect/loading scenarios (Fixes #861).

Changes:

• Add a typed handler for ClientKeepAlivePacket in ServerLoadingState and update latency/behind/simulation bookkeeping similarly to ServerPlayingState.
• Add a regression test client-state that sends a keepalive during the loading phase while the server is blocked waiting for join point completion.
• Add a server-side test covering the reconnect/loading keepalive scenario.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
Source/Common/Networking/State/ServerLoadingState.cs	Adds Client_KeepAlive handling during ServerLoading to avoid unhandled packet errors and keep timing/latency fields updated.
Source/Tests/ServerTest.cs	Adds a regression test intended to validate keepalive handling while waiting for join point completion.
Source/Tests/Helper/TestLoadingKeepAliveState.cs	Implements a test client connection state that sends Client_KeepAlive during the loading handshake.

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[Copilot]

The success condition here can be satisfied immediately because Players.Count starts at 0; the loop may break on the first iteration before the client has connected/sent any packets, so the test can pass without exercising the keepalive-in-loading behavior. Consider waiting until the player count becomes >0 (or another “client reached loading” signal) and only then waiting for it to drop back to 0 after disconnect.

[Copilot]

This fire-and-forget Task.Run isn’t awaited or tracked, so it can still execute after the test completes/teardown starts, potentially making the test nondeterministic and leaking work into subsequent tests. Store the task and await it (or add it to teardown) so join point completion is guaranteed and scoped to the test.

[Copilot]

Client_WorldRequest is sent reliably, but the keepalive is sent unreliably (reliable: false), so it can be delivered/processed before the world request and state transition on some transports. That can make the regression test flaky and may not guarantee the keepalive is handled specifically in ServerLoading. For determinism, send the keepalive reliably here (or otherwise synchronize so it’s sent only after the server has switched to loading).

Suggested change

	connection.Send(new ClientKeepAlivePacket(0, 0, false, 0), false);
	connection.Send(new ClientKeepAlivePacket(0, 0, false, 0));