Retain a stringbuilder to mutate the string rather than finalizing temporary strings
yields some speed improvements (less gen0 string objects allocated)
All logic in PokeCrypto is separate from the rest of the PKHeX.Core
library; makes it easy to just rip this portion out and reuse in other
projects without needing the entirety of PKHeX.Core logic
optimize out the CheckEncrypted to the actual path, separate methods.
Only usages of this method were with hardcoded Format values, so no
impact
remove Identifier param. 99% of the time, identifier is not provided,
resulting in a useless call
end result:
provide 'create new' and 'create from' constructors
