fix: Ensure _meta object is not lost when onprogress option is passed

When the onprogress option is passed, the _meta object in the request
params was being overwritten, causing any existing _meta content to be lost.

src/shared/protocol.ts

@@ -541,7 +541,10 @@ export abstract class Protocol<
         this._progressHandlers.set(messageId, options.onprogress);
         jsonrpcRequest.params = {
           ...request.params,
-          _meta: { progressToken: messageId },
+          _meta: {
+            ...(request.params._meta || {}),
+            progressToken: messageId
+          },
         };
       }