feat: add url property to RequestInfo interface

Expose the request URL in RequestInfo, allowing server handlers to access
query parameters, path info, and other URL components from incoming requests.

Author: valentinbeggi

.changeset/add-url-to-request-info.md

@@ -0,0 +1,5 @@
+---
+'@modelcontextprotocol/sdk': minor
+---
+
+Add `url` property to `RequestInfo` interface, exposing the request URL to server handlers