Rewrites a good amount of legality APIs pertaining to:
* Legal moves that can be learned
* Evolution chains & cross-generation paths
* Memory validation with forgotten moves
In generation 8, there are 3 separate contexts an entity can exist in: SW/SH, BD/SP, and LA. Not every entity can cross between them, and not every entity from generation 7 can exist in generation 8 (Gogoat, etc). By creating class models representing the restrictions to cross each boundary, we are able to better track and validate data.
The old implementation of validating moves was greedy: it would iterate for all generations and evolutions, and build a full list of every move that can be learned, storing it on the heap. Now, we check one game group at a time to see if the entity can learn a move that hasn't yet been validated. End result is an algorithm that requires 0 allocation, and a smaller/quicker search space.
The old implementation of storing move parses was inefficient; for each move that was parsed, a new object is created and adjusted depending on the parse. Now, move parse results are `struct` and store the move parse contiguously in memory. End result is faster parsing and 0 memory allocation.
* `PersonalTable` objects have been improved with new API methods to check if a species+form can exist in the game.
* `IEncounterTemplate` objects have been improved to indicate the `EntityContext` they originate in (similar to `Generation`).
* Some APIs have been extended to accept `Span<T>` instead of Array/IEnumerable
* Revises legality checks to account for traveling between the three game islands (PLA/BDSP/SWSH)
* Adds conversion mechanisms between the three formats, as well as flexible conversion options to backfill missing data (thanks GameFreak/ILCA for opting for lossy conversion instead of updating the games).
* Adds API abstractions for HOME data storage format (EKH/PKH format 1, aka EH1/PH1).
* Revises some APIs for better usage:
- `PKM` now exposes a `Context` to indicate the isolation context for legality purposes.
- Some method signatures have changed to accept `Context` or `GameVersion` instead of a vague `int` for Generation.
- Evolution History is now tracked in the Legality parse for specific contexts, rather than only per generation.
