chore: support MCP schema 2025-06-18 (#1621)

This updates the schema in `generate_mcp_types.py` from `2025-03-26` to
`2025-06-18`, regenerates `mcp-types/src/lib.rs`, and then updates all
the code that uses `mcp-types` to honor the changes.

Ran

```
npx @modelcontextprotocol/inspector just codex mcp
```

and verified that I was able to invoke the `codex` tool, as expected.


---
[//]: # (BEGIN SAPLING FOOTER)
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with [ReviewStack](https://reviewstack.dev/openai/codex/pull/1621).
* #1623
* #1622
* __->__ #1621

codex-rs/mcp-server/src/lib.rs

@@ -70,9 +70,7 @@ pub async fn run_main(codex_linux_sandbox_exe: Option<PathBuf>) -> IoResult<()>
                     JSONRPCMessage::Request(r) => processor.process_request(r),
                     JSONRPCMessage::Response(r) => processor.process_response(r),
                     JSONRPCMessage::Notification(n) => processor.process_notification(n),
-                    JSONRPCMessage::BatchRequest(b) => processor.process_batch_request(b),
                     JSONRPCMessage::Error(e) => processor.process_error(e),
-                    JSONRPCMessage::BatchResponse(b) => processor.process_batch_response(b),
                 }
             }