PR: Implement support for Astral's uv.

[KelSolaar]

This PR implements support for Astral's uv and drops support for Poetry.

• The pyproject.toml file is now much more standard and can use with many other tools.
• Assuming that uv is installed, OCIO View can now be launched as follows: uv run main.py.
• The virtual environment for development that now lives in the .venv directory next to the source, can be created as follows: uv sync --all-extras.

[doug-walker]

@KelSolaar , I checked with Michael, and he is fine with this. After you get back from vacation you may update the branch and merge it.

[carolalynn]

Hey @KelSolaar - still want to merge this?

[KelSolaar]

For sure yep!