ShowdownSet: Lessen allocation
MoveTutor: Remove boxing by calling the generic method instead of object method
Xoro8b: Add more xmldoc, use positive constant instead of inverse negative for parity
StadiumUtil: Use built-in endianness reversal methods
Existing `get`/`set` logic is flawed in that it doesn't work on Big Endian operating systems, and it allocates heap objects when it doesn't need to.
`System.Buffers.Binary.BinaryPrimitives` in the `System.Memory` NuGet package provides both Little Endian and Big Endian methods to read and write data; all the `get`/`set` operations have been reworked to use this new API. This removes the need for PKHeX's manual `BigEndian` class, as all functions are already covered by the BinaryPrimitives API.
The `StringConverter` has now been rewritten to accept a Span to read from & write to, no longer requiring a temporary StringBuilder.
Other Fixes included:
- The Super Training UI for Gen6 has been reworked according to the latest block structure additions.
- Cloning a Stadium2 Save File now works correctly (opening from the Folder browser list).
- Checksum & Sanity properties removed from parent PKM class, and is now implemented via interface.
Introducing a new PKM format: SK2
Split ICaughtData2 off of PK2 so it can be shared with SK2 when type-checks occur
Add conversion for PK2<->SK2
Split the split-buffer handling for GBPKM to GBPKML (what a name), so that I can reuse shared accessor logic for SK2.
