Warn on duplicate route names

[ahopkins]

Closes #2524

[codecov[bot]]

Codecov Report

Merging #2525 (6f39cee) into main (2f6f2bf) will increase coverage by 0.065%. The diff coverage is 100.000%.

@@              Coverage Diff              @@
##              main     #2525       +/-   ##
=============================================
+ Coverage   87.392%   87.457%   +0.065%     
=============================================
  Files           69        69               
  Lines         5560      5565        +5     
  Branches       966       969        +3     
=============================================
+ Hits          4859      4867        +8     
+ Misses         509       507        -2     
+ Partials       192       191        -1     

Impacted Files	Coverage Δ
sanic/app.py	88.825% <100.000%> (+0.106%)	:arrow_up:
sanic/server/protocols/http_protocol.py	83.823% <0.000%> (+2.205%)	:arrow_up:

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