Core topic
The entry point, and the logging every algorithm shares.
Fortis is the only class you construct from — Fortis.aes(), Fortis.rsa()
and Fortis.ecdh() each return the builder of one algorithm family, and every
type in the other categories is reached from one of them.
FortisLog carries the warnings the algorithms emit when a configuration is
legal but costly, such as generating an RSA key on Flutter web, where
dart:isolate is unavailable and the work runs on the main thread.