feat: provide more context information (#236)

* feat: provide more context information

1. provide context for notification
2. allow extract more info from tool call
3. inject http request part for streamable http server

* docs: add document for getting peer from context

crates/rmcp/src/model/extension.rs

@@ -49,7 +49,7 @@ pub struct Extensions {
 impl Extensions {
     /// Create an empty `Extensions`.
     #[inline]
-    pub fn new() -> Extensions {
+    pub const fn new() -> Extensions {
         Extensions { map: None }
     }