Remove dependency on pbr

[jugmac00]

... and instead use setuptools via pyproject.toml.

pbr does not seem to be well mainained any more, and using pyproject.toml is the modern approach to packaging in Python.

fixes #94

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This change is 

[jugmac00]

@jelmer I had a look at how hatchling is used in testtools, and there were a couple of things I am not familiar with, e.g. setuptools_scm, so for now I just migrated to setuptools via pyproject.toml analogous how it is done as in subunit. I hope that is ok.

[jugmac00]

Thanks for the review!

[jugmac00]

@jelmer I do not have merge permissions on this repo. Would you please merge the PR and create a new release? Thank you!

[bigjools]

Sorry I meant hatchling, not setuptools_scm!

[jelmer]

.

[jugmac00]

Thanks for the review. I applied the changes as requested. Please double check the version import, as that one is not entirely clear to me. I will squash the commits after a successful review.
@jelmer / @bigjools

[rbtcollins]

I'm confused here - pbr is still maintained. No objection to migrating, but the premise does seem inaccurate.

[jugmac00]

@rbtcollins Please see #94 (comment) - there is no support for Python 3.12 even that this version was released 1.5 years ago.

And I never claimed pbr is unmaintained, it is just not maintained well.

[jelmer]

The comment says to not track it, but it's checked in?

[jugmac00]

Thanks, removed it.

addressed by jugmac00

[jugmac00]

Thanks for merging, @jelmer. Would you be able to cut a new release?

[jelmer]

Thanks for merging, @jelmer. Would you be able to cut a new release?

I've done you one better and sent you an invite on pypi