feat: opt for concatenation instead of using fmt.Sprintf

baggage/baggage.go

@@ -335,9 +335,9 @@ func (m Member) String() string {
 	// A key is just an ASCII string. A value is restricted to be
 	// US-ASCII characters excluding CTLs, whitespace,
 	// DQUOTE, comma, semicolon, and backslash.
-	s := fmt.Sprintf("%s%s%s", m.key, keyValueDelimiter, valueEscape(m.value))
+	s := m.key + keyValueDelimiter + valueEscape(m.value)
 	if len(m.properties) > 0 {
-		s = fmt.Sprintf("%s%s%s", s, propertyDelimiter, m.properties.String())
+		s += propertyDelimiter + m.properties.String()
 	}
 	return s
 }

baggage/baggage_test.go

@@ -1027,3 +1027,18 @@ func BenchmarkValueEscape(b *testing.B) {
 		})
 	}
 }
+
+func BenchmarkMemberString(b *testing.B) {
+	b.ReportAllocs()
+	alphabet := "abcdefghijklmnopqrstuvwxyz"
+	props := make([]Property, len(alphabet))
+	for i, r := range alphabet {
+		props[i] = Property{key: string(r)}
+	}
+	member, err := NewMember(alphabet, alphabet, props...)
+	require.NoError(b, err)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = member.String()
+	}
+}