[#30] core/object: Implement raw object

Define RawObject type that inherits RawObject from NeoFS SDK. Implement
converters.

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

pkg/core/object/raw.go

@@ -0,0 +1,54 @@
+package object
+
+import (
+	"github.com/nspcc-dev/neofs-api-go/pkg/object"
+	objectV2 "github.com/nspcc-dev/neofs-api-go/v2/object"
+)
+
+// RawObject represents the raw NeoFS object.
+//
+// RawObject inherits RawObject type from NeoFS SDK.
+// It is used to implement some useful methods and functions
+// for convenient processing of a raw object by a node.
+type RawObject struct {
+	*object.RawObject
+}
+
+// NewRawFromV2 constructs RawObject instance from v2 Object message.
+func NewRawFromV2(obj *objectV2.Object) *RawObject {
+	return &RawObject{
+		RawObject: object.NewRawFromV2(obj),
+	}
+}
+
+// NewRawFrom constructs RawObject instance from NeoFS SDK RawObject.
+func NewRawFrom(obj *object.RawObject) *RawObject {
+	return &RawObject{
+		RawObject: obj,
+	}
+}
+
+// NewRaw constructs blank RawObject instance.
+func NewRaw() *RawObject {
+	return NewRawFrom(object.NewRaw())
+}
+
+// SDK converts RawObject to NeoFS SDK RawObject instance.
+func (o *RawObject) SDK() *object.RawObject {
+	if o != nil {
+		return o.RawObject
+	}
+
+	return nil
+}
+
+// Object converts RawObject to read-only Object instance.
+func (o *RawObject) Object() *Object {
+	if o != nil {
+		return &Object{
+			Object: o.RawObject.Object(),
+		}
+	}
+
+	return nil
+}