Update create_file to return TSourceFile (#219)

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Author: EdwardJXLi

src/codegen/sdk/core/codebase.py

@@ -391,7 +391,7 @@ def types(self) -> list[TTypeAlias]:
     # EXTERNAL API
     ####################################################################################################################
 
-    def create_file(self, filepath: str, content: str = "", sync: bool = True) -> File:
+    def create_file(self, filepath: str, content: str = "", sync: bool = True) -> TSourceFile:
         """Creates a new file in the codebase with specified content.
 
         Args: