perf(git): use 'uv.spawn' for command line IO

[linrongbin16]

Thanks to your contribute, while please finish below tasks:

Regression Test

Platforms

• windows
• macOS
• linux

Tasks

• Use <leader>gl to copy git link.
• Use <leader>gL to open git link in browser.
• Copy git link in a symlink directory of git repo.
• Copy git link in an un-pushed git branch, and receive an expected error.
• Copy git link in a pushed git branch but edited file, and receive a warning says the git link could be wrong.

[codecov]

Codecov Report

Attention: 55 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
lua/gitlinker.lua	32.86% <14.28%> (ø)
lua/gitlinker/git.lua	10.59% <21.42%> (+2.90%)	⬆️
lua/gitlinker/spawn.lua	78.57% <78.57%> (ø)

... and 3 files with indirect coverage changes

📢 Thoughts on this report? Let us know!.