Add a restart mechanism to all workers in the multiplexer

[ahopkins]

Closes #2619

This adds a app.m.restart(all_workers=True) flag.

[codecov]

Codecov Report

Base: 88.565% // Head: 88.568% // Increases project coverage by +0.003% 🎉

Coverage data is based on head (15ab517) compared to base (8e72036).
Patch coverage: 100.000% of modified lines in pull request are covered.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #2622       +/-   ##
=============================================
+ Coverage   88.565%   88.568%   +0.003%     
=============================================
  Files           81        81               
  Lines         6629      6631        +2     
  Branches      1128      1129        +1     
=============================================
+ Hits          5871      5873        +2     
  Misses         522       522               
  Partials       236       236               

Impacted Files	Coverage Δ
sanic/worker/multiplexer.py	100.000% <100.000%> (ø)

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