Refactor pokerus and add configs

[FosterProgramming]

Updated Pokerus to be able to config between different generations of Pokerus (This PR include test engine changes)

Description

I wanted to make the pokerus more readable/ easier to modify. To that effect, I did the following

• Moved the Pokerus functions to their own file
• Added 2 MON_DATA key to directly access the pokerus nibbles corresponding to the strain and numbers of days left
• Modified the random strain distribution to use a randomWeighted (the probabilities of each strain should be the same as before)
• All pokerus related functions have been refactores
• Tests have been added for all pokerus functions
• CHANGES TO THE TEST ENGINE were made to allow the pokerus tests to run

I also added new config to account for pokerus behavior in different generations based on the info in:
https://bulbapedia.bulbagarden.net/wiki/Pok%C3%A9rus

• a config to get infected by Pokerus while you have a pokemon with pokerus in your party (gen 2)
• a config to disable all pokerus effects similar (gen 9)
• a config for pokerus party spread to affect one pokemon at a time instead of two (gen 2)
• a config to choose the strain distriution of pokerus to match any generation
• a config to decide if pokerus gets a fresh timer when it spread in the player party (gen 2)
• a flag that can toggle pokerus infections (similar to gen 2 where pokerus can only infect pokemon after visiting goldenrod)
• configs to change spread and infection odds
• a config to disable pokemon having received pokerus reducing the odds of never infected pokemon catching pokerus
• a config to disable a rare case where pokerus timer can be overwritten by a pokemon having a different strain of pokerus
• a config to allow eggs to be infected or not

Media

Issue(s) that this PR fixes

#3908

Feature(s) this PR does NOT handle:

Features considered but not implemented in this PR:

• a config to choose if the pokemon center should tell the player about the pokerus (vanilla, she tells the player once, possibility to add option to never or always tell)
• a config to remove pokerus from the pokemon data/savebloock

Discord contact info

Jamie (foster_harmony)

[AlexOn1ine]

I don't know much about Pokerus so it's just a code review. Hope someone else takes over from here.