Avoid allocations with (*regexp.Regexp).MatchString

[Juneezee]

We should use (*regexp.Regexp).MatchString instead of (*regexp.Regexp).Match([]byte(...)) when matching string to avoid unnecessary []byte conversions and reduce allocations. A one-line change for free performance improvement.

Example benchmark:

var excludeRegex = regexp.MustCompile("vendor")

func BenchmarkMatch(b *testing.B) {
	for i := 0; i < b.N; i++ {
		if match := excludeRegex.Match([]byte("vendor/pkg/main.go")); !match {
			b.Fail()
		}
	}
}

func BenchmarkMatchString(b *testing.B) {
	for i := 0; i < b.N; i++ {
		if match := excludeRegex.MatchString("vendor/pkg/main.go"); !match {
			b.Fail()
		}
	}
}

Result:

goos: linux
goarch: amd64
pkg: github.com/boyter/scc/v3/processor
cpu: AMD Ryzen 7 PRO 4750U with Radeon Graphics
BenchmarkMatch-16          	 4123592	       274.9 ns/op	      24 B/op	       1 allocs/op
BenchmarkMatchString-16    	 7006401	       145.1 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/boyter/scc/v3/processor	2.637s

[boyter]

Oh yes very nice catch there. Thanks for submitting.