feat: add context_string function for formatted context information

Author: climbfuji

tools/write_standard_name_table.py

@@ -61,6 +61,12 @@ def convert_text_to_link(text_str):
     return link_str
 
 ########################################################################
+def context_string(context):
+    """Return a formatted string for context information."""
+    if context is None:
+        return ''
+    return f' at {context.filename}:{context.linenum}'
+
 def standard_name_to_long_name(prop_dict, context=None):
     """Translate a standard_name to its default long_name
     >>> standard_name_to_long_name({'standard_name':'cloud_optical_depth_layers_from_0p55mu_to_0p99mu'})