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_llm.py

@@ -13,12 +13,12 @@ from core.model_runtime.entities.llm_entities import LLMResult, LLMUsage
 from core.model_runtime.entities.message_entities import AssistantPromptMessage
 from core.workflow.entities.variable_pool import VariablePool
 from core.workflow.entities.workflow_node_execution import WorkflowNodeExecutionStatus
-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.event import RunCompletedEvent
 from core.workflow.nodes.llm.node import LLMNode
+from core.workflow.system_variable import SystemVariable
 from extensions.ext_database import db
 from models.enums import UserFrom
 from models.workflow import WorkflowType
@@ -62,12 +62,14 @@ def init_llm_node(config: dict) -> LLMNode:
 
     # construct variable pool
     variable_pool = VariablePool(
-        system_variables={
-            SystemVariableKey.QUERY: "what's the weather today?",
-            SystemVariableKey.FILES: [],
-            SystemVariableKey.CONVERSATION_ID: "abababa",
-            SystemVariableKey.USER_ID: "aaa",
-        },
+        system_variables=SystemVariable(
+            user_id="aaa",
+            app_id=app_id,
+            workflow_id=workflow_id,
+            files=[],
+            query="what's the weather today?",
+            conversation_id="abababa",
+        ),
         user_inputs={},
         environment_variables=[],
         conversation_variables=[],