namespace features are not correctly extracted across scopes

[williballenthin]

during the traige of #703, i've found that we don't correctly extract matched namespaces across scopes. that is, given a function-scope rule that matches, its namespaces are not extracted for matching at the file-scope.

this is relevant for the file limitation rules, e.g. "packer file limitation" (file-scope) that looks for namespace "anti-analysis/packer". this can match "packed with UPX" (file-scope) because the namespaces are extracted correctly within the same scope; however, "packed with generic packer" (function-scope) is not matched because the namespaces are not extracted from function scope into file scope.

this results in false negatives in which we'd expect some rules to match but they don't.