feat: use shallow git clone and shallow submodule clone

[roelofvandijk]

Pull Request Check List

Resolves: #2412
Relates to: #2094

This should speed up git clone for all large repositories.

I am unsure what extra tests would be required for this.
I am also not sure if there is any case in which a non-shallow clone of a repository would be required, for instance if tags are needed.

Note that --depth 1 automatically implies --single-branch per the git docs.

• Added tests for changed code.
• Updated documentation for changed code.

[roelofvandijk]

It seems like the --depth parameter is not recognized by the git command that is used in the tests. Is this a (very) old version of git? That could also cause some slowness for git clone.

[neersighted]

I'm not 100% sure this is something universally desirable to apply, and it will be need to done to Dulwich as well as the system git client. There should also be some fallback if it is not supported.

[mtkennerly]

I have a plugin that does VCS-based dynamic versioning, and this would break the handling for dependencies that also use the plugin. If you make this the default, please also add an option for Git dependencies to specify a custom depth, including the full history. For example:

[tool.poetry.dependencies]
requests = { git = "https://github.com/requests/requests.git", depth = 0 }

[github-actions]

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