feat: add an option to allow trailing slash insensitive matching

[charlie0129]

Add an option TrailingSlashInsensitivity in engine to allow trailing slash insensitive matching, e.g., if a handler for /path is defined, /path and /path/ will go the the same handler without redirection responses.

See the tests for details.

TrailingSlashInsensitivity is disabled by default so existing behavior should not be affected.

fixes #915

go test -benchmem -run="^$" -bench "^BenchmarkRouteTrailingSlashInsensitivity$" github.com/gin-gonic/gin
goos: linux
goarch: amd64
pkg: github.com/gin-gonic/gin
cpu: Intel(R) Xeon(R) Platinum 8352V CPU @ 2.10GHz
BenchmarkRouteTrailingSlashInsensitivity/Insensitive-144         	  116824	     10373 ns/op	    6238 B/op	      18 allocs/op
BenchmarkRouteTrailingSlashInsensitivity/Exact-144               	  116791	     10574 ns/op	    6237 B/op	      18 allocs/op
BenchmarkRouteTrailingSlashInsensitivity/Redirect-144            	   83282	     13627 ns/op	    6613 B/op	      27 allocs/op
PASS
ok  	github.com/gin-gonic/gin	3.987s

goos: darwin
goarch: arm64
pkg: github.com/gin-gonic/gin
cpu: Apple M2
BenchmarkRouteTrailingSlashInsensitivity/Insensitive-8         	  845089	      1404 ns/op	    6150 B/op	      18 allocs/op
BenchmarkRouteTrailingSlashInsensitivity/Exact-8               	  857839	      1461 ns/op	    6150 B/op	      18 allocs/op
BenchmarkRouteTrailingSlashInsensitivity/Redirect-8            	  674316	      1739 ns/op	    6474 B/op	      27 allocs/op
PASS
ok  	github.com/gin-gonic/gin	4.532

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.92%. Comparing base (3dc1cd6) to head (c3b1ea6).
Report is 148 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4306      +/-   ##
==========================================
- Coverage   99.21%   98.92%   -0.29%     
==========================================
  Files          42       44       +2     
  Lines        3182     3452     +270     
==========================================
+ Hits         3157     3415     +258     
- Misses         17       26       +9     
- Partials        8       11       +3     

Flag	Coverage Δ
	?
--ldflags="-checklinkname=0" -tags sonic	98.86% <100.00%> (?)
-tags go_json	98.86% <100.00%> (?)
-tags nomsgpack	98.91% <100.00%> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	?
go-1.23	98.92% <100.00%> (?)
go-1.24	98.92% <100.00%> (?)
macos-latest	98.92% <100.00%> (-0.29%)	⬇️
ubuntu-latest	98.92% <100.00%> (-0.29%)	⬇️

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[ddevsr]

	if length := len(p); length > 1 && p[length-1] == '/' {
		return p[:length-1];
	}

$ go test -run=^$ -bench='TrimWith' -benchmem
goos: windows
goarch: amd64
pkg: github.com/gin-gonic/gin
cpu: Intel(R) Core(TM) i5-3570 CPU @ 3.40GHz
BenchmarkTrimWithHasSuffix-4            100000000               11.13 ns/op            0 B/op          0 allocs/op
BenchmarkTrimWithManualCheck-4          1000000000               0.2761 ns/op          0 B/op          0 allocs/op
PASS
ok      github.com/PHPDevsr/gin-forked  1.586s

Keep this logic, faster than using strings.HasSuffix().

[charlie0129]

@ddevsr Hi, I kept the original logic