[#574] core: Extend Source interface with DeletionInfo method

* Introduce common method EverExisted
* Define DeletionInfo for struct that must implement Source
* Refactor tree srv

Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>

pkg/core/container/storage.go

@@ -41,6 +41,8 @@ type Source interface {
 	// Implementations must not retain the container pointer and modify
 	// the container through it.
 	Get(cid.ID) (*Container, error)
+
+	DeletionInfo(cid.ID) (*DelInfo, error)
 }
 
 // EACL groups information about the FrostFS container's extended ACL stored in

pkg/core/container/util.go

@@ -0,0 +1,22 @@
+package container
+
+import (
+	"errors"
+
+	apistatus "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client/status"
+	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
+)
+
+// EverExisted checks whether the container ever existed or
+// it just has not been created yet at the current epoch.
+func EverExisted(s Source, cid cid.ID) (bool, error) {
+	_, err := s.DeletionInfo(cid)
+	if err == nil {
+		return true, nil
+	}
+	var errContainerNotFound *apistatus.ContainerNotFound
+	if errors.As(err, &errContainerNotFound) {
+		return false, nil
+	}
+	return false, err
+}