Precalculate cfbd_pbp_data epa/wpa values to speed up data loading

[soricinae]

Is your feature request related to a problem? Please describe.
Today when I want epa or wpa data, I call cfbd_pbp_data for each week, sometimes going back several seasons. For each week, epa/wpa numbers are calculated by the function call, taking a minute or more per week.

Describe the solution you'd like
Precalculate the epa/wpa numbers and store them with the base data coming from the API. So when I call cfbd_pbp_data it only takes a few seconds to download the data from the API.

Describe alternatives you've considered
N/A

Additional context
nflfastr precalculates epa/wpa numbers which makes it quicker to get historical data.

[akeaswaran]

We should support this already via cfbfastR::load_cfb_pbp(). Have you tried that yet?