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/protocol/Cargo.toml

@@ -16,6 +16,7 @@ icu_decimal = { workspace = true }
 icu_locale_core = { workspace = true }
 mcp-types = { workspace = true }
 mime_guess = { workspace = true }
+paste = { workspace = true }
 serde = { workspace = true, features = ["derive"] }
 serde_json = { workspace = true }
 serde_with = { workspace = true, features = ["macros", "base64"] }