Issue Description

Problem:
When installing fusionrate directly from git using pip (e.g., pip install git+https://github.com/PrincetonUniversity/fusionrate.git), the package installs successfully but the critical data files in the fusionrate/data/ directory are missing, causing runtime errors.

Error encountered:

FileNotFoundError: [Errno 2] No such file or directory: '/path/to/site-packages/fusionrate/data/ions.json'

Expected behavior:
The data files (ions.json, cross_section_fits.csv, etc.) should be included in the installed package since they are essential for the package functionality.

Current workaround:
Users must manually download and copy the data files to the installation directory, which is not a clean solution.

Root cause:
The package's build configuration (likely missing proper MANIFEST.in or incomplete pyproject.toml package data specification) doesn't include the data files when building/installing from source.

Suggested fix:
Update the package configuration to properly include data files. This typically involves:

Updating pyproject.toml/setup.py to include:

[tool.setuptools.package-data]
fusionrate = ["data/*.json", "data/*.csv"]

Environment:

• Python: 3.13
• Installation method: pip install git+https://github.com/PrincetonUniversity/fusionrate.git
• OS: macOS (but likely affects all platforms)

This issue prevents users from installing fusionrate directly from the repository in clean environments or CI/CD pipelines.