Update request type on middleware types

[guacs]

Making the Request type generic while keeping it bound to Request on MiddlewareTypes allows users to subclass Sanic's Request class and use that to type hint their middleware functions. Now, when registering those middlewares, the type checkers would not complain.

This resolves #2753

[codecov]

Codecov Report

Patch coverage: 100.000% and project coverage change: +0.001 🎉

Comparison is base (049983c) 88.919% compared to head (7f06150) 88.920%.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #2754       +/-   ##
=============================================
+ Coverage   88.919%   88.920%   +0.001%     
=============================================
  Files           92        92               
  Lines         6976      6977        +1     
  Branches      1190      1190               
=============================================
+ Hits          6203      6204        +1     
  Misses         529       529               
  Partials       244       244               

Impacted Files	Coverage Δ
sanic/models/handler_types.py	100.000% <100.000%> (ø)

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