* Mystery Encounter bugfixes
* more ME bug fixes
* update allowed pokemon in ME requirements
* some unit test cleanup and general tidying
* fix null exception on isBattleMysteryEncounter
* clean up tsdocs and fix pokemon hasAbility check
* fix double battle crash in challenge mode with a single eligible pokemon
* apply suggestions from PR#4619's code reviews
* revert fix for Keldeo crashes + implement fix suggestion from PR #4619
* fix session migration for PokemonCustomData
* prevent test failure due to keldeo fix
---------
Co-authored-by: ImperialSympathizer <imperialsympathizer@gmail.com>