fix: ensure Decimal values in metadata are JSON serializable (fixes #19936) (#19955)

Co-authored-by: crazywoola <427733928@qq.com>

api/core/repositories/sqlalchemy_workflow_node_execution_repository.py

 from sqlalchemy.engine import Engine
 from sqlalchemy.orm import sessionmaker
 
+from core.model_runtime.utils.encoders import jsonable_encoder
 from core.workflow.entities.node_entities import NodeRunMetadataKey
 from core.workflow.entities.node_execution_entities import (
     NodeExecution,
         db_model.status = domain_model.status
         db_model.error = domain_model.error
         db_model.elapsed_time = domain_model.elapsed_time
-        db_model.execution_metadata = json.dumps(domain_model.metadata) if domain_model.metadata else None
+        db_model.execution_metadata = (
+            json.dumps(jsonable_encoder(domain_model.metadata)) if domain_model.metadata else None
+        )
         db_model.created_at = domain_model.created_at
         db_model.created_by_role = self._creator_user_role
         db_model.created_by = self._creator_user_id

api/tests/unit_tests/repositories/workflow_node_execution/test_sqlalchemy_repository.py

 
 import json
 from datetime import datetime
+from decimal import Decimal
 from unittest.mock import MagicMock, PropertyMock
 
 import pytest
 from pytest_mock import MockerFixture
 from sqlalchemy.orm import Session, sessionmaker
 
+from core.model_runtime.utils.encoders import jsonable_encoder
 from core.repositories import SQLAlchemyWorkflowNodeExecutionRepository
 from core.workflow.entities.node_entities import NodeRunMetadataKey
 from core.workflow.entities.node_execution_entities import NodeExecution, NodeExecutionStatus
         status=NodeExecutionStatus.RUNNING,
         error=None,
         elapsed_time=1.5,
-        metadata={NodeRunMetadataKey.TOTAL_TOKENS: 100},
+        metadata={NodeRunMetadataKey.TOTAL_TOKENS: 100, NodeRunMetadataKey.TOTAL_PRICE: Decimal("0.0")},
         created_at=datetime.now(),
         finished_at=None,
     )
     assert db_model.inputs_dict == domain_model.inputs
     assert db_model.process_data_dict == domain_model.process_data
     assert db_model.outputs_dict == domain_model.outputs
-    assert db_model.execution_metadata_dict == domain_model.metadata
+    assert db_model.execution_metadata_dict == jsonable_encoder(domain_model.metadata)
 
     assert db_model.status == domain_model.status
     assert db_model.error == domain_model.error