[FEAT] Add both: traditional and usernameless / accountless authentication

[egregors]

One of the goal of this lib is to provide simple but flexible way to build apps with Passkey. In this case, it should give to consumers a choice: usual or accountless auth.

As far as we have two ways to auth, API handlers should be acting a bit different. That why it could be not so easy to implement universal enough handlers to cover both scenario. Probably I should make separate set of handlers.

• [BUG] Respect user.id | name | displayName in traditional auth flow #31
• [FEAT] Support resident keys (RKs) and non-resident keys (NRKs)  #32

Right now, I don't really sure, if I want to support traditional auth way.