use uv

[jpn--]

This pull request modernizes the CI workflow and project configuration for the SANDAG ABM3 example. The main focus is on migrating the environment setup from Conda to uv and standardizing Python version management, with additional improvements to dependency specification and test configuration.

CI workflow modernization:

• Migrated the CI environment setup in .github/workflows/ci.yml from Conda to uv, including installation steps for uv, syncing dependencies via uv sync, and using uv pip install for installing ActivitySim. Removed all Conda-specific steps and caching logic.
• Updated the Python version management in the CI workflow to use .python-version and the setup-python action’s python-version-file option, ensuring Python 3.11 is consistently used. [1] [2]

Project configuration and dependencies:

• Added a new pyproject.toml specifying project metadata, core dependencies, and a development dependency group, making the environment reproducible and easier to manage.

Testing configuration:

• Updated the path for importing extensions in the test suite (test/test_sandag_abm3.py) from "../extensions" to "extensions", aligning with the new project structure.