[codex] Preserve crossbar simulation results and remove noisy gateway log

[tamlut-modnys]

Summary

• preserve server-provided result values in both mirrored Rust Crossbar clients for Solana and Sui simulation responses
• only compute the Solana median fallback when result is absent
• remove the unconditional gateway URL log in both mirrored Rust Gateway clients without changing FetchSignaturesConsensusParams
• add mirrored static regression tests covering empty results, server-result precedence, median fallback, and Sui decimal-string deserialization

Why

Crossbar can return results: [] while still providing a string result. The current Rust clients were dropping that server-provided value, and MarginFi PR #5 only fixed one of the two mirrored surfaces. MarginFi PR #9 also addressed a real logging annoyance, but did it by adding a field to a public params struct, which would be a downstream breaking change.

This keeps the useful behavior from both proposals while avoiding the public API break.

Validation

• cargo test --locked --manifest-path solana/rust/switchboard-on-demand-client/Cargo.toml
  • new Crossbar regression tests passed
  • full command still fails on pre-existing doctests in solana/rust/switchboard-on-demand-client/src/lib.rs
• cargo test --locked --no-default-features --features client --manifest-path solana/rust/switchboard-on-demand/Cargo.toml
  • passed
• cargo check --locked --no-default-features --features client-v3 --manifest-path solana/rust/switchboard-on-demand/Cargo.toml
  • still fails in untouched surge.rs, subscription.rs, utils.rs, and transaction_builder.rs