[mini.diff] Add customization options to gen_source.git

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• I have read CODE_OF_CONDUCT.md

Module(s)

mini.diff

Description

My use case is fairly straight forward: I use yadm (Yet Another Dotfiles Manager), and I want mini.diff to work reliably.

yadm is essentially a wrapper around git where the repo directory and the work directory differ.

Currently, I'm doing a copy and paste of all of the git functionality from mini.diff to create a yadm source, and replacing all of the references to git with yadm, but that's a pain to maintain, and really, it should be unnecessary.

The only thing that I need to be able to customize is the git command itself, though, if I were implementing this as a general thing, I'd add the ability to add custom arguments to all command runs as well.

Ideally, I would be able to do something like:

      source = {
        MiniDiff.gen_source.git(),
        MiniDiff.gen_source.git({git_cmd = "yadm"}),
        MiniDiff.gen_source.save(),
      },

Read the mini.diff module's MiniDiff.gen_source.git implementation and trace how it constructs each git command. Determine how the requested git_cmd option should apply while preserving the existing default behavior. Done means yadm can use the same source functionality without copying the git implementation.