Color descriptor-backed gRPC JSON output

[ryanfowler]

Summary

• Thread stdout color policy into streamed gRPC formatting
• Render descriptor-backed gRPC frames through the JSON formatter so keys and values are colored consistently
• Update gRPC integration coverage to expect colored streamed JSON in a PTY

Testing

• cargo fmt --check
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --locked --all-features --lib --bins
• cargo test --locked --all-features --test grpc