Remove Sendable requirements on Authenticatable

[0xTim]

Removes the requirement for Authenticatable types to be Sendable which was causing issues with Fluent models (and any reference types) and wasn't solvable in a non-breaking way.

This uses an unsafe box to wrap the Authenticatable types which removes compiler checking on usage of the box but should not be an issue due to the way Vapor's auth is implemented

[codecov-commenter]

Codecov Report

Merging #3095 (e290104) into main (3bf4e73) will increase coverage by 0.00%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3095   +/-   ##
=======================================
  Coverage   76.23%   76.24%           
=======================================
  Files         211      211           
  Lines        7904     7906    +2     
=======================================
+ Hits         6026     6028    +2     
  Misses       1878     1878           

Files	Coverage Δ
...ces/Vapor/Authentication/AuthenticationCache.swift	84.84% <100.00%> (+0.97%)	⬆️
Sources/Vapor/Authentication/Authenticator.swift	57.89% <ø> (ø)
Sources/Vapor/Authentication/GuardMiddleware.swift	100.00% <ø> (ø)
...rces/Vapor/Authentication/RedirectMiddleware.swift	83.33% <ø> (ø)

[gwynne]

One tiny nit, just to be annoying 🙂

[0xTim]

Of course 😛

[penny-for-vapor]

These changes are now available in 4.85.1