chore: use a single buffer for field checks (#16)

Instead of creating a new string every for each possible version of a
field we now (re-)use a single byte array to do the same.

Benchmark comparison is:
```
goos: linux
goarch: amd64
pkg: github.com/terramate-io/tfjson/v2/sanitize
cpu: 13th Gen Intel(R) Core(TM) i7-13620H
                  │   v2.txt    │              v2_pr.txt              │
                  │   sec/op    │   sec/op     vs base                │
LargeChangeset-16   24.55µ ± 6%   13.01µ ± 2%  -46.99% (p=0.000 n=10)

                  │   v2.txt    │             v2_pr.txt              │
                  │    B/op     │    B/op     vs base                │
LargeChangeset-16   7672.0 ± 0%   784.0 ± 0%  -89.78% (p=0.000 n=10)

                  │   v2.txt    │             v2_pr.txt              │
                  │  allocs/op  │ allocs/op   vs base                │
LargeChangeset-16   368.00 ± 0%   42.00 ± 0%  -88.59% (p=0.000 n=10)
```

Before:
```
goos: linux
goarch: amd64
pkg: github.com/terramate-io/tfjson/v2/sanitize
cpu: 13th Gen Intel(R) Core(TM) i7-13620H
BenchmarkLargeChangeset
BenchmarkLargeChangeset-16    	   46780	     22959 ns/op	    7672 B/op	     368 allocs/op
BenchmarkLargeChangeset-16    	   45748	     23622 ns/op	    7672 B/op	     368 allocs/op
BenchmarkLargeChangeset-16    	   51043	     24620 ns/op	    7672 B/op	     368 allocs/op
BenchmarkLargeChangeset-16    	   48404	     23003 ns/op	    7672 B/op	     368 allocs/op
BenchmarkLargeChangeset-16    	   44822	     25041 ns/op	    7672 B/op	     368 allocs/op
BenchmarkLargeChangeset-16    	   46743	     24831 ns/op	    7672 B/op	     368 allocs/op
BenchmarkLargeChangeset-16    	   51252	     25010 ns/op	    7672 B/op	     368 allocs/op
BenchmarkLargeChangeset-16    	   48674	     23974 ns/op	    7672 B/op	     368 allocs/op
BenchmarkLargeChangeset-16    	   45248	     24541 ns/op	    7672 B/op	     368 allocs/op
BenchmarkLargeChangeset-16    	   50532	     24560 ns/op	    7672 B/op	     368 allocs/op
PASS
ok  	github.com/terramate-io/tfjson/v2/sanitize	14.217s
```

With PR:
```
goos: linux
goarch: amd64
pkg: github.com/terramate-io/tfjson/v2/sanitize
cpu: 13th Gen Intel(R) Core(TM) i7-13620H
BenchmarkLargeChangeset
BenchmarkLargeChangeset-16    	   88532	     12938 ns/op	     784 B/op	      42 allocs/op
BenchmarkLargeChangeset-16    	   88912	     13293 ns/op	     784 B/op	      42 allocs/op
BenchmarkLargeChangeset-16    	   91579	     13061 ns/op	     784 B/op	      42 allocs/op
BenchmarkLargeChangeset-16    	   91285	     12980 ns/op	     784 B/op	      42 allocs/op
BenchmarkLargeChangeset-16    	   91048	     13062 ns/op	     784 B/op	      42 allocs/op
BenchmarkLargeChangeset-16    	   91712	     12895 ns/op	     784 B/op	      42 allocs/op
BenchmarkLargeChangeset-16    	   91569	     12948 ns/op	     784 B/op	      42 allocs/op
BenchmarkLargeChangeset-16    	   91477	     13012 ns/op	     784 B/op	      42 allocs/op
BenchmarkLargeChangeset-16    	   91344	     13227 ns/op	     784 B/op	      42 allocs/op
BenchmarkLargeChangeset-16    	   91731	     13015 ns/op	     784 B/op	      42 allocs/op
PASS
ok  	github.com/terramate-io/tfjson/v2/sanitize	13.270s
```

Author: boekkooi-terramate

sanitize/sanitize_change.go

@@ -60,27 +60,28 @@ func sanitizeChangeValue(old, sensitive, replaceWith interface{}) interface{} {
 	return old
 }
 
-var sanitizeAuxiliaryPostfix = []string{
-	"_base64",
-	"_base64sha1",
-	"_base64sha256",
-	"_base64sha512",
-	"_md5",
-	"_sha1",
-	"_sha256",
-	"_sha512",
+var sanitizeAuxiliaryPostfix = [][]byte{
+	[]byte("_base64"),
+	[]byte("_base64sha1"),
+	[]byte("_base64sha256"),
+	[]byte("_base64sha512"),
+	[]byte("_md5"),
+	[]byte("_sha1"),
+	[]byte("_sha256"),
+	[]byte("_sha512"),
 }
 
 func sanitizeAuxiliary(field string, values map[string]interface{}, sensitive, replaceWith interface{}) {
 	if val, ok := sensitive.(bool); !ok || !val {
 		return
 	}
 
-	var auxField string
+	auxField := []byte(field)
+	auxFieldLen := len(auxField)
 	for _, aux := range sanitizeAuxiliaryPostfix {
-		auxField = field + aux
-		if val, ok := values[auxField]; ok && val != nil {
-			values[auxField] = replaceWith
+		auxField = append(auxField[:auxFieldLen], aux...)
+		if val, ok := values[string(auxField)]; ok && val != nil {
+			values[string(auxField)] = replaceWith
 		}
 	}
 }