Ability to import def pfr data

[felixblochwitz]

This PR addresses issue #108

It adds the option to specify s_type as def for the functions import_seasonal_pfr and import_weekly_pfr by adding them as valid inputs to the function _validate_pfr_inputs.

Data for defensive stats is available since 2018 (same starting point as other categories) here: https://github.com/nflverse/nflverse-data/releases/tag/pfr_advstats. Thus, loading this data should work as intended.

[alecglen]

Looks good, thanks @felixblochwitz!

[alecglen]

I changed the PR's base branch from main to v0.3.3 so it will merge in with the next package version being released this week. If you merge that branch's commits into your branch, then the test suite should pass and we'll get this merged.

[felixblochwitz]

I changed the PR's base branch from main to v0.3.3 so it will merge in with the next package version being released this week. If you merge that branch's commits into your branch, then the test suite should pass and we'll get this merged.

Thanks for your comment. I think I merged the commits from the v0.3.3 branch successfully into my branch (hope I did this correctly, it's my first time contributing to something public). If you need me to do anything else, just let me know.

[alecglen]

Perfect - thanks again! 👍