Split headers by single space, handle trimming

Author: mikeas1

src/a2a/server/apps/jsonrpc/jsonrpc_app.py

@@ -104,9 +104,10 @@ def build(self, request: Request) -> ServerCallContext:
             user=user,
             state=state,
             requested_extensions={
-                ext
+                stripped
                 for h in request.headers.getlist(HTTP_EXTENSION_HEADER)
-                for ext in h.split(', ')
+                for ext in h.split(',')
+                if (stripped := ext.strip())
             },
         )