Use Unix Domain Sockets in RPCChainVM

[joshua-kim]

VMs currently only work over the same host, so there isn't a reason to use TCP sockets over domain sockets. Domain sockets can have performance benefits over the current approach as there isn't any overhead of TCP as domain sockets already have ordered and reliable properties as they are implemented over files.

[hexfusion]

The original plan that @StephenButtolph and I talked about was to use unix abstract sockets. The issue was lack of support from Rust.[1] There does seem to be a workaround which I will create an issue for in avalanche-rs to track.

[1] tokio-rs/tokio#4610

[github-actions]

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