Use bytes.Buffer from stack buf in Matcher.String()

Also removed the growing until there's a benchmark for that.

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

model/labels/matcher.go

@@ -14,8 +14,8 @@
 package labels
 
 import (
+	"bytes"
 	"strconv"
-	"unsafe"
 )
 
 // MatchType is an enum for label matching types.
@@ -79,20 +79,19 @@ func MustNewMatcher(mt MatchType, name, val string) *Matcher {
 }
 
 func (m *Matcher) String() string {
-	const quote = 1
-	const matcher = 2
-	// As we're not on go1.22 yet and we don't have the new fancy AvailableBuffer method on strings.Builder,
-	// we'll use a plain byte slice and then do the unsafe conversion to string just like strings.Builder does.
-	// We pre-allocate pessimistically for quoting the label name, and optimistically for not having to escape any quotes.
-	b := make([]byte, 0, quote+len(m.Name)+quote+matcher+quote+len(m.Value)+quote)
+	// Start a buffer with a pre-allocated size on stack to cover most needs.
+	var bytea [1024]byte
+	b := bytes.NewBuffer(bytea[:0])
+
 	if m.shouldQuoteName() {
-		b = strconv.AppendQuote(b, m.Name)
+		b.Write(strconv.AppendQuote(b.AvailableBuffer(), m.Name))
 	} else {
-		b = append(b, m.Name...)
+		b.WriteString(m.Name)
 	}
-	b = append(b, m.Type.String()...)
-	b = strconv.AppendQuote(b, m.Value)
-	return *((*string)(unsafe.Pointer(&b)))
+	b.WriteString(m.Type.String())
+	b.Write(strconv.AppendQuote(b.AvailableBuffer(), m.Value))
+
+	return b.String()
 }
 
 func (m *Matcher) shouldQuoteName() bool {