Stats test cases

[Walnut356]

I was hesitant to make these while I was changing the stats fields so often. Now that they're changing less often, it's probably a good idea to make some tests for the following:

• Each stat processes all the way through without errors
• get_stats can process several replays without getting stuck
• Each stat output matches a pre-verified output. The easiest way to go about this is making a 10 second or so replay vs a CPU with a few instances of the event. To save work in the future, it might be worth only comparing the number of rows, or rows + some columns that aren't going anywhere, since otherwise it will fail and need updating if a new column is ever added.

I also wouldn't mind some more replays of older slippi versions, but I can probably just grab those from slippi.gg's tournament sets.