fix: guard MoveToStandbyState in async void transition methods

[Qian-Cheng-nju]

Hi, thanks for dotNext again!

The three async void state transition methods (MoveToFollowerState, MoveToCandidateState, MoveToLeaderState) call MoveToStandbyState() in their catch blocks as a fallback. If MoveToStandbyState() itself throws (e.g., DisposeAsync failure during UpdateStateAsync), the exception escapes the async void method and crashes the process via the unobserved exception handler.

This wraps each MoveToStandbyState() fallback in a try-catch so the exception is logged instead of crashing.

[Qian-Cheng-nju]

@dotnet-policy-service agree [company="{Nanjing University}"]

[Qian-Cheng-nju]

@dotnet-policy-service agree company="Nanjing University"

[sakno]

DisposeAsync as well as Dispose must be idempotent and exception-free. This is recommended not only for Raft, it is for all implementations of IDisposable and IAsyncDisposable interfaces. In .NEXT Raft, every Raft state is designed in that way. It's better to analyze their implementations to achieve the necessary behavior rather than assuming the exception.

[Qian-Cheng-nju]

You're right — I checked all four state implementations and their DisposeAsyncCore() methods are fully guarded with try-catch-finally. There's no path that can throw. Thanks for the explanation!