feature: Improve recognition of functions through assignments

[pawamoy]

Is your feature request related to a problem? Please describe.

Functions created using partial are not recognized as functions but as attributes. mkdocstrings renders them as attributes, which is not great.

Describe the solution you'd like

Ideally Griffe would support partial-like things from the standard lib to transform such attributes into functions. Maybe this should be supported through an extension, like for dataclasses, depending on the difficulty of merging signatures of the partial and the function passed as argument (which could be a partial too).

Describe alternatives you've considered

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Additional context

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