refactor(api): Separate SegmentType for Integer/Float to Enable Pydantic Serialization (#22025)

refactor(api): Separate SegmentType for Integer/Float to Enable Pydantic Serialization (#22025)

This PR addresses serialization issues in the VariablePool model by separating the `value_type` tags for `IntegerSegment`/`FloatSegment` and `IntegerVariable`/`FloatVariable`. Previously, both Integer and Float types shared the same `SegmentType.NUMBER` tag, causing conflicts during serialization.

Key changes:
- Introduce distinct `value_type` tags for Integer and Float segments/variables
- Add `VariableUnion` and `SegmentUnion` types for proper type discrimination
- Leverage Pydantic's discriminated union feature for seamless serialization/deserialization
- Enable accurate serialization of data structures containing these types

Closes #22024.

api/tests/integration_tests/workflow/nodes/test_http.py

@@ -6,11 +6,11 @@ import pytest
 
 from core.app.entities.app_invoke_entities import InvokeFrom
 from core.workflow.entities.variable_pool import VariablePool
-from core.workflow.enums import SystemVariableKey
 from core.workflow.graph_engine.entities.graph import Graph
 from core.workflow.graph_engine.entities.graph_init_params import GraphInitParams
 from core.workflow.graph_engine.entities.graph_runtime_state import GraphRuntimeState
 from core.workflow.nodes.http_request.node import HttpRequestNode
+from core.workflow.system_variable import SystemVariable
 from models.enums import UserFrom
 from models.workflow import WorkflowType
 from tests.integration_tests.workflow.nodes.__mock.http import setup_http_mock
@@ -44,7 +44,7 @@ def init_http_node(config: dict):
 
     # construct variable pool
     variable_pool = VariablePool(
-        system_variables={SystemVariableKey.FILES: [], SystemVariableKey.USER_ID: "aaa"},
+        system_variables=SystemVariable(user_id="aaa", files=[]),
         user_inputs={},
         environment_variables=[],
         conversation_variables=[],