Switch from poetry to uv

[JWCook]

Closes #365

Changes

• use uv + hatchling for project & build config
• update CI config:
  • use uv to install python instead of actions/setup-python
  • add python 3.14-rc2 to test matrix
  • use uvx with toml-cli to set pre-release versions
  • updated publish step to use PyPI trusted publishing (replaces API tokens)
• update contributing guide
• replace poetry run -> uv run
• readthedocs build: replace poetry export -> uv export

[alessio-locatelli]

I executed the unit tests in a fresh virtual environment, and I reviewed the GitHub Actions and all other files. Everything appears to be okay.

As a small note, I want to mention that uv has not reached its first major release; therefore, unexpected breaking changes may occur.