[#752] innerring: Optimize keyPosition()

```
goos: linux
goarch: amd64
pkg: git.frostfs.info/TrueCloudLab/frostfs-node/pkg/innerring
cpu: 11th Gen Intel(R) Core(TM) i5-1135G7 @ 2.40GHz
              │      old       │                 new                 │
              │     sec/op     │   sec/op     vs base                │
KeyPosition-8   2771.50n ± 10%   40.32n ± 4%  -98.55% (p=0.000 n=10)

              │     old      │                  new                  │
              │     B/op     │     B/op      vs base                 │
KeyPosition-8   1.531Ki ± 0%   0.000Ki ± 0%  -100.00% (p=0.000 n=10)

              │    old     │                new                 │
              │ allocs/op  │ allocs/op  vs base                 │
KeyPosition-8   21.00 ± 0%   0.00 ± 0%  -100.00% (p=0.000 n=10)
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/innerring/indexer.go

@@ -1,7 +1,6 @@
 package innerring
 
 import (
-	"bytes"
 	"fmt"
 	"sync"
 	"time"
@@ -113,10 +112,9 @@ func (s *innerRingIndexer) AlphabetIndex() (int32, error) {
 // index of the key.
 func keyPosition(key *keys.PublicKey, list keys.PublicKeys) (result int32) {
 	result = -1
-	rawBytes := key.Bytes()
 
 	for i := range list {
-		if bytes.Equal(list[i].Bytes(), rawBytes) {
+		if key.Equal(list[i]) {
 			result = int32(i)
 			break
 		}

pkg/innerring/indexer_test.go

@@ -223,3 +223,23 @@ func (f *testIRFetcher) InnerRingKeys() (keys.PublicKeys, error) {
 	f.calls.Add(1)
 	return f.keys, f.err
 }
+
+func BenchmarkKeyPosition(b *testing.B) {
+	list := make(keys.PublicKeys, 7)
+	for i := range list {
+		p, err := keys.NewPrivateKey()
+		require.NoError(b, err)
+		list[i] = p.PublicKey()
+	}
+
+	key := new(keys.PublicKey)
+	require.NoError(b, key.DecodeBytes(list[5].Bytes()))
+
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		if keyPosition(key, list) != 5 {
+			b.FailNow()
+		}
+	}
+}