Add PokemonStatPast

[jemarq04]

This PR addresses issue #1325 and adds a new model: PokemonStatPastto store changes to base stats and EV yields over generations. The new model came with a new CSV file: pokemon_stats_past.csv.

In addition to these additions, the following changes were made:

• Added migration needed before any changes were made (0024 was created before I made changes.. maybe missing from a recent PR?)
• Added new special stat to track generation 1 stat spread.
• Update EV yields that changed in generation 9 (wyrdeer, kleavor, basculegion-male, basculegion-female, sneasler, overqwil, and enamorus-therian)

Information retrieved from the different pages linked in https://bulbapedia.bulbagarden.net/wiki/List_of_Pok%C3%A9mon_by_effort_value_yield_in_Generation_IX and https://bulbapedia.bulbagarden.net/wiki/Base_stats#Changes.

Edited to reflect current state of PR.

[jemarq04]

Upon further reflection, I think even though the stats are different and EV yields didn’t exist in generation 1, it may be best to have all information in PokemonStatPast. I’ll revert this to a draft and do some checks to make sure that should work smoothly before submitting this for review again.

[jemarq04]

No changes were changed between generation 1 and 2 other than the splitting of the special stat, so instead of a separate field for original stats I just added the special stat as an entry in the past stats field. Should be all settled now!

[Naramsim]

ok, thanks again. I'll take some time to understand what's going on!

[jemarq04]

I edited the initial PR description to make it clearer since I made a big change after the fact - as always if you have questions/suggestions let me know!