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/IO/AdaptiveReadBufferTests.cs

@@ -0,0 +1,17 @@
+using NATS.Server.IO;
+
+namespace NATS.Server.Transport.Tests;
+
+public class AdaptiveReadBufferTests
+{
+    [Fact]
+    public void Read_buffer_scales_between_512_and_65536_based_on_recent_payload_pattern()
+    {
+        var b = new AdaptiveReadBuffer();
+        b.RecordRead(512);
+        b.RecordRead(4096);
+        b.RecordRead(32000);
+        b.CurrentSize.ShouldBeGreaterThan(4096);
+        b.CurrentSize.ShouldBeLessThanOrEqualTo(64 * 1024);
+    }
+}