rmcp 3.3.0 adds enterprise token exchanges and an initialize negotiation hook

The official Rust SDK released rmcp 3.3.0 on 2026-09-10. ServerHandler::negotiate_initialize is a new hook (#1247), and the macros crate now rejects an empty tool_router at build time (#1233).

Under auth, the release adds enterprise refresh-token and ID-JAG token exchanges (#1234) and unifies refresh checks and error handling across the crate (#1236).

One fix closes a crash path: SSE reconnect backoff now saturates instead of overflowing, which could otherwise panic after enough failed reconnect attempts (#1231). The release follows rmcp 3.2.0, which coordinated OAuth token refreshes through credential stores and added request-state key rotation, ten days earlier.