chore: add #[non_exhaustive] and mutation methods to improve compatibility (#715)

* chore: add #[non_exhaustive] to reduce backwards-incompatible changes going forward

* fix: remove ProtocolVersion import

* fix: add a few more with_ mutator methods

---------

Co-authored-by: Alex Hancock <alexhancock@block.xyz>

crates/rmcp/tests/test_client_initialization.rs

@@ -1,4 +1,6 @@
 // cargo test --features "server client" --package rmcp test_client_initialization
+#![cfg(feature = "client")]
+
 mod common;
 
 use std::borrow::Cow;