Add better error messaging when starting a surfnet on the same port as another network

[MicaiahReid]

Just hit this today, it happen when you have more than one surfpool running. So workaround is kill the old process.

Originally posted by @katopz in #331

[GauravBurande]

https://github.com/txtx/surfpool/blob/92e9df6a3fdf8545e18c53f4cfcf0f406d68be0b/crates/core/src/rpc/full.rs#L1615 is this where this error is being handled?

[MicaiahReid]

No, this error should be returned on startup, not when a transaction fails to be processed.

If you try to start a surfnet and the port is already being used, we should return an error

[Pawank06]

gm @GauravBurande are you working on this issue?

[GauravBurande]

yeah, but u can go ahead, I'm not able to find source.

[Pawank06]

yeah, but u can go ahead, I'm not able to find source.

ok