fix: use macros to ensure request/response symmetry (#4529)

Manually curating `protocol-ts/src/lib.rs` was error-prone, as expected.
I finally asked Codex to write some Rust macros so we can ensure that:

- For every variant of `ClientRequest` and `ServerRequest`, there is an
associated `params` and `response` type.
- All response types are included automatically in the output of `codex
generate-ts`.

codex-rs/Cargo.toml

@@ -123,6 +123,7 @@ opentelemetry-semantic-conventions = "0.30.0"
 opentelemetry_sdk = "0.30.0"
 os_info = "3.12.0"
 owo-colors = "4.2.0"
+paste = "1.0.15"
 path-absolutize = "3.1.1"
 path-clean = "1.0.1"
 pathdiff = "0.2"