Add comment about enum performance

Author: mcollins-ttd

uid2_client/input_util.py

@@ -22,6 +22,10 @@ def is_phone_number_normalized(phone_number):
     return min_phone_number_digits <= total_digits <= max_phone_number_digits
 
 
+# Accessing an enum member is ~3x slower than accessing a non-enum member in Python 3.11.
+# This was improved in Python 3.12 but there's still a performance overhead (~44% slower).
+# That's why this class isn't an enum.
+# https://github.com/python/cpython/issues/93910#issuecomment-1165503032
 class EmailParsingState:
     Starting = 1
     Pre = 2