feat(chore): singleflight when request backend multiple time at once #1267

Job	Run time
Check that Souin build as caddy module	6m 53s
Check that Souin build as middleware / Check that Souin build as Dotweb middleware	2m 50s
Check that Souin build as middleware / Check that Souin build as Beego middleware	56s
Check that Souin build as middleware / Check that Souin build as Echo middleware	2m 47s
Check that Souin build as middleware / Check that Souin build as Chi middleware	2m 31s
Check that Souin build as middleware / Check that Souin build as Gin middleware	2m 46s
Check that Souin build as middleware / Check that Souin build as Fiber middleware	2m 43s
Check that Souin build as middleware / Check that Souin build as Goa middleware	2m 51s
Check that Souin build as middleware / Check that Souin build as Go-zero middleware	4m 14s
Check that Souin build as middleware / Check that Souin build as Kratos middleware	2m 46s
Check that Souin build as middleware / Check that Souin build as Roadrunner middleware	48s
Check that Souin build as middleware / Check that Souin build as Skipper middleware	2m 50s
Check that Souin build as middleware / Check that Souin build as Hertz middleware	2m 16s
Check that Souin build as middleware / Check that Souin build as Souin middleware	3m 4s
Check that Souin build as middleware / Check that Souin build as Traefik middleware	6h 0m 20s
Check that Souin build as middleware / Check that Souin build as Tyk middleware	4m 4s
Check that Souin build as middleware / Check that Souin build as Webgo middleware	2m 45s
	6h 47m 24s

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