fix(logging): add "Tool" type to message sender labeling (#1412)

Previously, messages of type "tool" were not distinctly labeled in the
LoggingCallbackHandler output, causing them to be grouped under
"System".
This change adds explicit handling for "tool" messages, labeling them as
"Tool" in the logs for improved clarity and debugging.

Author: Pouyanpi

tests/test_callbacks.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from unittest.mock import patch
 from uuid import uuid4
 
 import pytest