Add error variant for connection errors for Remote Prover

A user may want to use the remote prover and fallback to a local prover if the connection is failing. In that scenario, the user would match the error returned by the prover. Currently, all connection errors are encompassed into the `TransactionProverError::Other` variant, with a string message explaining the error. Would be nice to add a new variant for this.

https://github.com/0xMiden/miden-node/blob/66c0bbdd74e95ca0a09737f8105c09d62563965a/crates/remote-prover-client/src/remote_prover/tx_prover.rs#L97-L99

cc @sergerad in case I'm missing something?