Fixed Proxy when using MultipartForm with byte[] (#473)

* wip

* ByteArrayContentHelper

* ByteArrayContentHelperTests

test/WireMock.Net.Tests/Http/ByteArrayContentHelperTests.cs

@@ -0,0 +1,44 @@
+using System.Net.Http.Headers;
+using System.Text;
+using System.Threading.Tasks;
+using FluentAssertions;
+using WireMock.Http;
+using Xunit;
+
+namespace WireMock.Net.Tests.Http
+{
+    public class ByteArrayContentHelperTests
+    {
+        [Fact]
+        public async Task ByteArrayContentHelperTests_Create_WithNullContentType()
+        {
+            // Arrange
+            var content = Encoding.UTF8.GetBytes("test");
+
+            // Act
+            var result = ByteArrayContentHelper.Create(content, null);
+
+            // Assert
+            result.Headers.ContentType.Should().BeNull();
+            (await result.ReadAsByteArrayAsync()).Should().BeEquivalentTo(content);
+        }
+
+        [Theory]
+        [InlineData("application/octet-stream", "application/octet-stream")]
+        [InlineData("application/soap+xml", "application/soap+xml")]
+        [InlineData("multipart/form-data; boundary=------------------------x", "multipart/form-data; boundary=------------------------x")]
+        public async Task ByteArrayContentHelperTests_Create(string test, string expected)
+        {
+            // Arrange
+            var content = Encoding.UTF8.GetBytes("test");
+            var contentType = MediaTypeHeaderValue.Parse(test);
+
+            // Act
+            var result = ByteArrayContentHelper.Create(content, contentType);
+
+            // Assert
+            result.Headers.ContentType.ToString().Should().Be(expected);
+            (await result.ReadAsByteArrayAsync()).Should().BeEquivalentTo(content);
+        }
+    }
+}