[benches] Update RPC benches for current client API

[washanhanzi]

Summary

This updates the RPC benchmark code to match the current connectrpc client API. The client-stream benchmarks now call client_stream(messages) without redundant default call options, the manual bidi benchmark request uses connectrpc::client::full_body(...), and the stale CallOptions import was removed.

Why

The benchmark code had drifted behind the current client API and helper usage.

Impact

The RPC benchmark crate builds cleanly against the current API, keeping the benchmark suite aligned with the library surface.

Root cause

The benchmark code still referenced an older client-stream call shape and body-construction path after the client helpers changed.

Validation

• cargo check --manifest-path benches/rpc/Cargo.toml --benches

[github-actions]

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[washanhanzi]

I have read the CLA Document and I hereby sign the CLA

[washanhanzi]

recheck

[iainmcgin]

Thanks for the contribution! In #25 I'll enable --all-targets to avoid this regressing again in future.