Exp/compress candidates (#942)

* Compress block candidates in validator-session

* Compress blocks in full-node (disabled for now)

---------

Co-authored-by: SpyCheese <mikle98@yandex.ru>

tdutils/td/utils/lz4.h

@@ -0,0 +1,27 @@
+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+*/
+#pragma once
+
+#include "td/utils/buffer.h"
+#include "td/utils/Status.h"
+
+namespace td {
+
+td::BufferSlice lz4_compress(td::Slice data);
+td::Result<td::BufferSlice> lz4_decompress(td::Slice data, int max_decompressed_size);
+
+}  // namespace td