Fix polyhedron error, improve UX for CifEnsemble, fix histogram label

[bobleesj]

Fixed the following issues

• https://github.com/bobleesj/cifkit/issues/10
• https://github.com/bobleesj/cifkit/issues/11
• https://github.com/bobleesj/cifkit/issues/12
• https://github.com/bobleesj/cifkit/issues/13
• https://github.com/bobleesj/cifkit/issues/14
• https://github.com/bobleesj/cifkit/issues/15
• Use pyproject.toml to install packages in GitHub Actions

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 98.96907% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.15%. Comparing base (aa21e2d) to head (f558f65).

Files	Patch %	Lines
tests/core/models/test_cif.py	96.15%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #17 +/- ## ========================================== + Coverage 97.07% 97.15% +0.08% ========================================== Files 34 34 Lines 1297 1337 +40 ========================================== + Hits 1259 1299 +40 Misses 38 38 ```

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