fix(boc): correct offsetBytes computation; add regression tests

TonSdk.Core/src/boc/BOC.cs

@@ -277,8 +277,9 @@ public static Bits SerializeBoc(
             }
 
             var dataBits = dataBuilder.Build();
-            var offsetBytes = Math.Max((dataBits.Length.bitLength() + 7) / 8, 1);
-
+            var dataBytesSize = Math.Max((dataBits.Length + 7) / 8, 1) ; 
+            var offsetBytes = Math.Max((dataBytesSize.bitLength() + 7) / 8, 1);
+
             /*
               serialized_boc#b5ee9c72 has_idx:(## 1) has_crc32c:(## 1)
                                       has_cache_bits:(## 1) flags:(## 2) { flags = 0 }

TonSdk.Core/test/boc/Cell.test.cs

@@ -1,8 +1,56 @@
 using TonSdk.Core.Boc;
 
-namespace TonSdk.Core.Tests;
+namespace TonSdk.Core.Tests.Boc;
 
+public class CellTest
+{
+    [Test]
+    public void SerializeTest()
+    {
+        // Arrange
+        const int sampleValue = 0x32fab9;
+        var builder = new CellBuilder();
 
-public class CellTest {
+        // Store the same 32-bit value 8 times (total: 256 bits)
+        for (var i = 0; i < 8; i++)
+        {
+            builder.StoreUInt(sampleValue, 32);
+        }
 
-}
+        // Expected BoC produced by @ton/core (JavaScript):
+        // b.toBoc().toString("hex")
+        const string expectedBoc =
+            "b5ee9c724101010100220000400032fab90032fab90032fab90032fab90032fab90032fab90032fab90032fab979fc9ee0";
+
+        // Act
+        var cell = builder.Build();
+        var boc = cell.ToString("hex").ToLowerInvariant();
+
+        // Assert
+        Assert.That(boc, Is.EqualTo(expectedBoc));
+    }
+
+    [Test]
+    public void DeserializeTest()
+    {
+        // Arrange
+        const string boc =
+            "b5ee9c724101010100220000400032fab90032fab90032fab90032fab90032fab90032fab90032fab90032fab979fc9ee0";
+
+        const int sampleValue = 0x32fab9;
+
+        // Act
+        var cell = Cell.From(new Bits(Convert.FromHexString(boc)));
+        var slice = cell.Parse();
+
+        // Assert
+        // 8 values * 32 bits each = 256 bits remaining
+        Assert.That(slice.RemainderBits, Is.EqualTo(32 * 8));
+
+        for (var i = 0; i < 8; i++)
+        {
+            var value = (int)slice.LoadUInt(32);
+            Assert.That(value, Is.EqualTo(sampleValue));
+        }
+    }
+}