Add a rule to exclude functions under a namespace

[ametel01]

Add a rule here https://github.com/crytic/amarna/blob/2bb48690eae625737bb59b84e1961795528f7bc8/amarna/rules/post_process_rules/UnusedFunctionsRule.py#L30 to exclude, function under namespace in libraries, from being flagged with “unused function” warning.