refactor: Reorganize project to use uv and uv_build

[nvictus]

• Move source root to src directory
• Switch from hatch to uv for project management.
• Switch from hatchling to uv_build build backend. This isn't really necessary. Hatchling works fine, and we can switch back if we ever need plugins or hooks.
• Replace development-related "extras" with PEP 735 dependency groups
  • e.g. pip install --group dev . will install all the test, dev, and doc dependencies
  • uv sync will automatically use the dev dependency group
• Remove hatch scripts and document commands in CONTRIBUTING.md
• Add python 3.13 to CI
• Update deprecated sphinx extension configurations and readthedocs.yml (fix missing project name)