fix: add check to ensure output of generate_mcp_types.py matches codex-rs/mcp-types/src/lib.rs (#3450)

As a follow-up to https://github.com/openai/codex/pull/3439, this adds a
CI job to ensure the codegen script has to be updated in order to change
`codex-rs/mcp-types/src/lib.rs`.

.github/workflows/rust-ci.yml

@@ -62,6 +62,8 @@ jobs:
           components: rustfmt
       - name: cargo fmt
         run: cargo fmt -- --config imports_granularity=Item --check
+      - name: Verify codegen for mcp-types
+        run: ./mcp-types/check_lib_rs.py
 
   cargo_shear:
     name: cargo shear