Fix Pydantic field alias consistency in structured output

Resolve inconsistency between schema and actual output when using Pydantic models with field aliases as tool return types:
- Add by_alias=True parameter to model_dump() call in func_metadata.py
- Add comprehensive test case to verify alias consistency
- Ensure schema generation and structured output use same aliased field names

Before: Schema shows "first", "second" but output uses "field_first", "field_second"
After: Both schema and output consistently use aliased field names

Author: sjwhole

src/mcp/server/fastmcp/utilities/func_metadata.py

@@ -111,7 +111,7 @@ def convert_result(self, result: Any) -> Any:
 
             assert self.output_model is not None, "Output model must be set if output schema is defined"
             validated = self.output_model.model_validate(result)
-            structured_content = validated.model_dump(mode="json")
+            structured_content = validated.model_dump(mode="json", by_alias=True)
 
             return (unstructured_content, structured_content)