refactor: extract NATS.Server.Transport.Tests project

Move TLS, OCSP, WebSocket, Networking, and IO test files from
NATS.Server.Tests into a dedicated NATS.Server.Transport.Tests
project. Update namespaces, replace private GetFreePort/ReadUntilAsync
with shared TestUtilities helpers, extract TestCertHelper to
TestUtilities, and replace Task.Delay polling loops with
PollHelper.WaitUntilAsync/YieldForAsync for proper synchronization.

tests/NATS.Server.Transport.Tests/WebSocket/WsFrameReadTests.cs

@@ -0,0 +1,163 @@
+using System.Buffers.Binary;
+using NATS.Server.WebSocket;
+using Shouldly;
+
+namespace NATS.Server.Transport.Tests.WebSocket;
+
+public class WsFrameReadTests
+{
+    /// <summary>Helper: build a single unmasked binary frame.</summary>
+    private static byte[] BuildFrame(byte[] payload, bool fin = true, bool compressed = false, int opcode = WsConstants.BinaryMessage, bool mask = false, byte[]? maskKey = null)
+    {
+        int payloadLen = payload.Length;
+        byte b0 = (byte)opcode;
+        if (fin) b0 |= WsConstants.FinalBit;
+        if (compressed) b0 |= WsConstants.Rsv1Bit;
+        byte b1 = 0;
+        if (mask) b1 |= WsConstants.MaskBit;
+
+        byte[] lenBytes;
+        if (payloadLen <= 125)
+        {
+            lenBytes = [(byte)(b1 | (byte)payloadLen)];
+        }
+        else if (payloadLen < 65536)
+        {
+            lenBytes = new byte[3];
+            lenBytes[0] = (byte)(b1 | 126);
+            BinaryPrimitives.WriteUInt16BigEndian(lenBytes.AsSpan(1), (ushort)payloadLen);
+        }
+        else
+        {
+            lenBytes = new byte[9];
+            lenBytes[0] = (byte)(b1 | 127);
+            BinaryPrimitives.WriteUInt64BigEndian(lenBytes.AsSpan(1), (ulong)payloadLen);
+        }
+
+        int totalLen = 1 + lenBytes.Length + (mask ? 4 : 0) + payloadLen;
+        var frame = new byte[totalLen];
+        frame[0] = b0;
+        lenBytes.CopyTo(frame.AsSpan(1));
+        int pos = 1 + lenBytes.Length;
+        if (mask && maskKey != null)
+        {
+            maskKey.CopyTo(frame.AsSpan(pos));
+            pos += 4;
+            var maskedPayload = payload.ToArray();
+            WsFrameWriter.MaskBuf(maskKey, maskedPayload);
+            maskedPayload.CopyTo(frame.AsSpan(pos));
+        }
+        else
+        {
+            payload.CopyTo(frame.AsSpan(pos));
+        }
+        return frame;
+    }
+
+    [Fact]
+    public void ReadSingleUnmaskedFrame()
+    {
+        var payload = "Hello"u8.ToArray();
+        var frame = BuildFrame(payload);
+
+        var readInfo = new WsReadInfo(expectMask: false);
+        var stream = new MemoryStream(frame);
+        var result = WsReadInfo.ReadFrames(readInfo, stream, frame.Length, maxPayload: 1024);
+
+        result.Count.ShouldBe(1);
+        result[0].ShouldBe(payload);
+    }
+
+    [Fact]
+    public void ReadMaskedFrame()
+    {
+        var payload = "Hello"u8.ToArray();
+        byte[] key = [0x37, 0xFA, 0x21, 0x3D];
+        var frame = BuildFrame(payload, mask: true, maskKey: key);
+
+        var readInfo = new WsReadInfo(expectMask: true);
+        var stream = new MemoryStream(frame);
+        var result = WsReadInfo.ReadFrames(readInfo, stream, frame.Length, maxPayload: 1024);
+
+        result.Count.ShouldBe(1);
+        result[0].ShouldBe(payload);
+    }
+
+    [Fact]
+    public void Read16BitLengthFrame()
+    {
+        var payload = new byte[200];
+        Random.Shared.NextBytes(payload);
+        var frame = BuildFrame(payload);
+
+        var readInfo = new WsReadInfo(expectMask: false);
+        var stream = new MemoryStream(frame);
+        var result = WsReadInfo.ReadFrames(readInfo, stream, frame.Length, maxPayload: 1024);
+
+        result.Count.ShouldBe(1);
+        result[0].ShouldBe(payload);
+    }
+
+    [Fact]
+    public void ReadPingFrame_ReturnsPongAction()
+    {
+        var frame = BuildFrame([], opcode: WsConstants.PingMessage);
+
+        var readInfo = new WsReadInfo(expectMask: false);
+        var stream = new MemoryStream(frame);
+        var result = WsReadInfo.ReadFrames(readInfo, stream, frame.Length, maxPayload: 1024);
+
+        result.Count.ShouldBe(0); // control frames don't produce payload
+        readInfo.PendingControlFrames.Count.ShouldBe(1);
+        readInfo.PendingControlFrames[0].Opcode.ShouldBe(WsConstants.PongMessage);
+    }
+
+    [Fact]
+    public void ReadCloseFrame_ReturnsCloseAction()
+    {
+        var closePayload = new byte[2];
+        BinaryPrimitives.WriteUInt16BigEndian(closePayload, 1000);
+        var frame = BuildFrame(closePayload, opcode: WsConstants.CloseMessage);
+
+        var readInfo = new WsReadInfo(expectMask: false);
+        var stream = new MemoryStream(frame);
+        var result = WsReadInfo.ReadFrames(readInfo, stream, frame.Length, maxPayload: 1024);
+
+        result.Count.ShouldBe(0);
+        readInfo.CloseReceived.ShouldBeTrue();
+        readInfo.CloseStatus.ShouldBe(1000);
+    }
+
+    [Fact]
+    public void ReadPongFrame_NoAction()
+    {
+        var frame = BuildFrame([], opcode: WsConstants.PongMessage);
+
+        var readInfo = new WsReadInfo(expectMask: false);
+        var stream = new MemoryStream(frame);
+        var result = WsReadInfo.ReadFrames(readInfo, stream, frame.Length, maxPayload: 1024);
+
+        result.Count.ShouldBe(0);
+        readInfo.PendingControlFrames.Count.ShouldBe(0);
+    }
+
+    [Fact]
+    public void Unmask_Optimized_8ByteChunks()
+    {
+        byte[] key = [0xAA, 0xBB, 0xCC, 0xDD];
+        var original = new byte[32];
+        Random.Shared.NextBytes(original);
+        var masked = original.ToArray();
+
+        // Mask it
+        for (int i = 0; i < masked.Length; i++)
+            masked[i] ^= key[i & 3];
+
+        // Unmask using the state machine
+        var info = new WsReadInfo(expectMask: true);
+        info.SetMaskKey(key);
+        info.Unmask(masked);
+
+        masked.ShouldBe(original);
+    }
+}