Fix routing conflict for dynamic routes and static route with common prefix (#1509)

[lammel]

This PR resolves issue #1509

A routing conflict is caused by radix tree node splits on common prefix of static routes together with a param route on the same level. An additional test has been added for this issue.

This patch actually ensures that routing will continue back up the route tree in that case.

[codecov]

Codecov Report

Merging #1512 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1512   +/-   ##
=======================================
  Coverage   84.54%   84.54%           
=======================================
  Files          27       27           
  Lines        2097     2097           
=======================================
  Hits         1773     1773           
  Misses        211      211           
  Partials      113      113

Impacted Files	Coverage Δ
router.go	97.13% <100%> (ø)	⬆️

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[lammel]

This PR has an impact on the routing performance of ~15% in the worst case.
Numbers are taken using the available test benchmarks on my local system.

Before the patch (master, f4b5a90):

sh# /usr/bin/go test -benchmem -run=^$ github.com/labstack/echo/v4 -bench ^(BenchmarkRouterStaticRoutes|BenchmarkRouterGitHubAPI|BenchmarkRouterParseAPI|BenchmarkRouterGooglePlusAPI)$

goos: linux
goarch: amd64
pkg: github.com/labstack/echo/v4
BenchmarkRouterStaticRoutes-16     	   66543	     17475 ns/op	       0 B/op	       0 allocs/op
BenchmarkRouterGitHubAPI-16        	   31058	     38630 ns/op	       2 B/op	       0 allocs/op
BenchmarkRouterParseAPI-16         	  174482	      5884 ns/op	       0 B/op	       0 allocs/op
BenchmarkRouterGooglePlusAPI-16    	  123810	      9144 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/labstack/echo/v4	5.274s

With this patch applied:

sh# /usr/bin/go test -benchmem -run=^$ github.com/labstack/echo/v4 -bench ^(BenchmarkRouterStaticRoutes|BenchmarkRouterGitHubAPI|BenchmarkRouterParseAPI|BenchmarkRouterGooglePlusAPI)$

goos: linux
goarch: amd64
pkg: github.com/labstack/echo/v4
BenchmarkRouterStaticRoutes-16     	   56984	     20068 ns/op	       1 B/op	       0 allocs/op
BenchmarkRouterGitHubAPI-16        	   26817	     44528 ns/op	       2 B/op	       0 allocs/op
BenchmarkRouterParseAPI-16         	  192571	      5751 ns/op	       0 B/op	       0 allocs/op
BenchmarkRouterGooglePlusAPI-16    	  100843	     11578 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/labstack/echo/v4	5.476s

[lammel]

Managed to save some CPU cylces by avoiding backing up the tree for static only route trees (where no next param or any nodes are stored)

goos: linux
goarch: amd64
pkg: github.com/labstack/echo/v4
BenchmarkRouterStaticRoutes-16     	   63564	     18446 ns/op	       0 B/op	       0 allocs/op
BenchmarkRouterGitHubAPI-16        	   27559	     43419 ns/op	       2 B/op	       0 allocs/op
BenchmarkRouterParseAPI-16         	  194587	      5777 ns/op	       0 B/op	       0 allocs/op
BenchmarkRouterGooglePlusAPI-16    	  107343	     11036 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/labstack/echo/v4	5.501s

[vishr]

@lammel Thanks for your work!