Fix issue 7

[Adam-Hoelscher]

Functional changes in these files

• pyproject.toml
• src/tryangle/ensemble/base.py
• src/tryangle/metrics/score.py
• tests/test_ensemble.py
• tox.ini

These and several other files also have whitespace changes created by black.

Added sparse<0.16 to tox.ini, which has tradeoffs

• Pro: tests pass
• Con: since it's not actually in requirements, it doesn't ensure that the PyPI published version will work. Alternatively, we could add this to pyproject.toml and publish to PyPI immediately.

[cbalona]

Hi Adam, thanks very much for the changes. Happy with them. I did have failed tests on py3.13 with chainladder<0.8.20 however. I plan to do a review of the full codebase this year and fix some deepre issues. We can limit python to <3.13 for now until then. I also agree with adding to pypi with the limitation on chainladder.