[#922] storage engine: Prevent any operations after first Close call

Make `BlockExecution` / `ResumeExecution` to not release per-shard worker
pools. Make `StorageEngine.Close` to block these methods and any
data-related operations. It is still releases the pools.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/local_object_storage/engine/control_test.go

@@ -0,0 +1,46 @@
+package engine
+
+import (
+	"errors"
+	"testing"
+
+	cidtest "github.com/nspcc-dev/neofs-api-go/pkg/container/id/test"
+	"github.com/stretchr/testify/require"
+)
+
+func TestExecBlocks(t *testing.T) {
+	e := testNewEngineWithShardNum(t, 2) // number doesn't matter in this test, 2 is several but not many
+	defer e.Close()
+
+	// put some object
+	obj := generateRawObjectWithCID(t, cidtest.Generate()).Object()
+
+	addr := obj.Address()
+
+	require.NoError(t, Put(e, obj))
+
+	// block executions
+	errBlock := errors.New("block exec err")
+
+	require.NoError(t, e.BlockExecution(errBlock))
+
+	// try to exec some op
+	_, err := Head(e, addr)
+	require.ErrorIs(t, err, errBlock)
+
+	// resume executions
+	require.NoError(t, e.ResumeExecution())
+
+	_, err = Head(e, addr) // can be any data-related op
+	require.NoError(t, err)
+
+	// close
+	require.NoError(t, e.Close())
+
+	// try exec after close
+	_, err = Head(e, addr)
+	require.Error(t, err)
+
+	// try to resume
+	require.Error(t, e.ResumeExecution())
+}