Add the option to define dependency groups

[befeleme]

In the specfiles

%pyproject_buildrequires -g tests

More info: https://peps.python.org/pep-0735/

[befeleme]

Additional notes:

• this is only defined in pyproject.toml, doesn't propagate to core metadata, hence implementing will require looking to the insides of sdists

  • pyp2spec doesn't download and store anything at the user's drive yet, this could be an overkill
  • maybe after Create spec files from local packages #53? pyp2spec will already be inspecting wheels, sdists lay just next to them;
    • that would divert the capabilities based on the data source (local with dep. groups, pypi without - so back to the previous problem)

• no need to go deeper than the group names, no need for any kind of value evaluation; the example below should result in extracting group-a, group-b, group-c and all.

[dependency-groups]
group-a = ["foo"]
group-b = ["foo>1.0"]
group-c = ["foo<1.0"]
all = ["foo", {include-group = "group-a"}, {include-group = "group-b"}, {include-group = "group-c"}]