all: use new AppendEncode methods available in Go 1.22 (#11079)

Updates #cleanup

Signed-off-by: Joe Tsai <joetsai@digital-static.net>

types/key/util.go

@@ -53,18 +53,10 @@ func clamp25519Private(b []byte) {
 func appendHexKey(dst []byte, prefix string, key []byte) []byte {
 	dst = slices.Grow(dst, len(prefix)+hex.EncodedLen(len(key)))
 	dst = append(dst, prefix...)
-	dst = hexAppendEncode(dst, key)
+	dst = hex.AppendEncode(dst, key)
 	return dst
 }
 
-// TODO(https://go.dev/issue/53693): Use hex.AppendEncode instead.
-func hexAppendEncode(dst, src []byte) []byte {
-	n := hex.EncodedLen(len(src))
-	dst = slices.Grow(dst, n)
-	hex.Encode(dst[len(dst):][:n], src)
-	return dst[:len(dst)+n]
-}
-
 // parseHex decodes a key string of the form "<prefix><hex string>"
 // into out. The prefix must match, and the decoded base64 must fit
 // exactly into out.