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

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

crates/rmcp/src/model/annotated.rs

@@ -11,6 +11,7 @@ use super::{
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Default)]
 #[serde(rename_all = "camelCase")]
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
+#[non_exhaustive]
 pub struct Annotations {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub audience: Option<Vec<Role>>,