perf(otelstorage): increase Attrs on-stack sorting threshold

```
cpu: AMD Ryzen 9 5950X 16-Core Processor
                  │   old.txt   │            new.txt            │
                  │   sec/op    │   sec/op     vs base          │
InserterTraces-32   557.1µ ± 1%   553.5µ ± 1%  ~ (p=0.081 n=15)

                  │   old.txt    │               new.txt                │
                  │     B/op     │     B/op      vs base                │
InserterTraces-32   56.02Ki ± 0%   28.29Ki ± 0%  -49.50% (p=0.000 n=15)

                  │   old.txt   │              new.txt              │
                  │  allocs/op  │ allocs/op   vs base               │
InserterTraces-32   1009.0 ± 0%   969.0 ± 0%  -3.96% (p=0.000 n=15)
```

internal/chstorage/attributes_json.go

@@ -74,8 +74,10 @@ func encodeMap(e *jx.Encoder, m pcommon.Map, additional ...[2]string) {
 		value value
 	}
 	var pairs []pair
-	if l := m.Len(); l < 16 {
-		pairs = make([]pair, 0, 16)
+
+	const stackThreshold = otelstorage.MapStackThreshold
+	if l := m.Len(); l < stackThreshold {
+		pairs = make([]pair, 0, stackThreshold)
 	} else {
 		pairs = make([]pair, 0, m.Len()+len(additional))
 	}

internal/otelstorage/hash.go

@@ -18,6 +18,9 @@ func (h Hash) String() string {
 	return hex.EncodeToString(h[:])
 }
 
+// MapStackThreshold defines common constant for on-stack [Attrs] sorting.
+const MapStackThreshold = 32
+
 // AttrHash computes attributes hash.
 func AttrHash(m pcommon.Map) Hash {
 	h := xxh3.New()
@@ -74,8 +77,8 @@ func hashMap(h *xxh3.Hasher, m pcommon.Map) {
 		value pcommon.Value
 	}
 	var pairs []pair
-	if l := m.Len(); l < 16 {
-		pairs = make([]pair, 0, 16)
+	if l := m.Len(); l < MapStackThreshold {
+		pairs = make([]pair, 0, MapStackThreshold)
 	} else {
 		pairs = make([]pair, 0, m.Len())
 	}