Most potential deadlock problems should have been fixed, and new code is
unlikely to cause new problems with the new design.
Also raise the minimum Git version required to 2.6.0 (released in 2015)
Refactor Git command functions to use WithXXX methods instead of
exposing RunOpts.
This change simplifies reuse across gitrepo and improves consistency,
encapsulation, and maintainability of command options.
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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
