Update rmcp to 1.8.0 (#29634)

## Summary

- Update `rmcp` and `rmcp-macros` from 1.7.0 to 1.8.0.
- Adapt to the new shared `peer_info` return type.
- Box OAuth status discovery at the MCP boundary to keep the expanded
future type from overflowing Rust's trait recursion limit.

This brings in custom OAuth HTTP client support from
[modelcontextprotocol/rust-sdk#908](https://github.com/modelcontextprotocol/rust-sdk/pull/908).

codex-rs/codex-mcp/src/mcp/auth.rs

@@ -10,6 +10,7 @@ use codex_protocol::protocol::McpAuthStatus;
 use codex_rmcp_client::OAuthProviderError;
 use codex_rmcp_client::determine_streamable_http_auth_status;
 use codex_rmcp_client::discover_streamable_http_oauth;
+use futures::FutureExt;
 use futures::future::join_all;
 use tracing::warn;
 
@@ -217,6 +218,7 @@ async fn compute_auth_status(
                 store_mode,
                 keyring_backend_kind,
             )
+            .boxed()
             .await
         }
     }