Relocate checksum adders to Checksums class, improve performance by eliminating slice calls
Improve HOME sharing for GO8 and IMoveset encounters: actually sanity check GO8, and skip other non-PK7/PB7 cases.
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.
Further improvements can be made if there's a way to have a union struct (4 u16s, lumped u64) that has a simple 4bit diagonal mirror operation on it. Can be at least twice as fast.
Benchmarking with optimizations shows about 80-90% of the prior time taken, so at least a 10% speed optimization
Rarely used, was fun to try and optimize a little more.
Eliminate bounds checks by accessing/setting the highest element, and only index twice instead of 6x.
Eliminate u16 casts by leaving as int type (same result)
Eliminate temp value caching and instead directly write to storage. (no more _0123).
End result looks neat too, since the >> 0's removed looks like a diagonal, like the nibble rotation :D
