Reject network account mutations in RPC

[AlgofootPrint]

Summary

• reject submitted transactions when an existing non-network account delta touches the standardized network-account allowlist slot
• apply the same RPC-side check to each transaction in submitted batches
• add focused unit coverage for the rejection path and existing network-account allowance

Part of #2146.

Testing

• git diff --check passes, with line-ending warnings only
• cargo test -p miden-node-rpc server::api::tests could not complete because miden-node-proto-build failed first: file 'C:\Users\damio\Desktop\PR\node\proto\proto\remote_prover.proto' is not in any include path

[Mirko-von-Leipzig]

Diffs in the other files seem unrelated to this PR.

[Mirko-von-Leipzig]

This diff seem unrelated

[AlgofootPrint]

My apologies, that came from an unrelated commit that was accidentally included underneath this branch.

I rebased the PR onto current next and force-pushed a cleaned version. The diff is now scoped to the RPC-side rejection for #2146 and no longer includes crates/store/src/state/mod.rs.