feat(ntx): export NtxAuth and implement RPC client

[igamigo]

While testing 0xMiden/miden-client#2203, I realized we needed NtxAuth exported for bootstrapping the testing node easily, so I made that change in this branch.
When testing that implementation, noticed the NTX-related tests were failing so looking into it I realized the RPC client was missing, so I made a first implementation. Opening as draft because client integration tests are still not passing.

[Mirko-von-Leipzig]

While testing 0xMiden/miden-client#2203, I realized we needed NtxAuth exported for bootstrapping the testing node easily, so I made that change in this branch.

I'm not quite following the flow here - do you manually submit ntx yourselves to get things into a certain state?

I thought we were switching to the docker compose setup, but that's currently in a broken state pending #2159 and #2160

[igamigo]

client integration tests are still not passing.

What was missing here was adding the genesis commitment to the RPC client's accept header settings.

I'm not quite following the flow here - do you manually submit ntx yourselves to get things into a certain state?

From before, we were manually setting up the processes for our testing node, which allowed us to configure various things (haven't looked at migrating to the docker setup). Now, for starting the RPC process we need to set the ntx auth headers which requires that struct if we want to do it in Rust:

            Rpc {
                listener: grpc_rpc,
                ...
                network_tx_auth: Some(NetworkTxAuth(ntx_auth_header)),
            }