Allow selectable default on infer_file_format

Author: rocky

mathics/eval/fileformats/compression.py

@@ -68,7 +68,7 @@ def eval_ImportZIP(
 
             for element in elements:
                 member = element.value
-                file_format = infer_file_format(member).upper()
+                file_format = infer_file_format(member, "Text").upper()
                 if file_format not in IMPORTERS.keys():
                     evaluation.message("Import", "fmtnosup", file_format)
                     return SymbolFailed

mathics/eval/import_export/importexport.py

@@ -696,10 +696,10 @@ def eval_Import_source_only(
         return result
 
 
-def infer_file_format(filename: str) -> Optional[str]:
+def infer_file_format(filename: str, default_extension: str = None) -> Optional[str]:
     """
     Infer what kind of format filename is in. None is returned if we can't infer
     a format.
     """
     file_extension = eval_FileExtension(filename).lower()
-    return FILE_EXTENSION_MAP.get(file_extension, "Text")
+    return FILE_EXTENSION_MAP.get(file_extension, default_extension)