refactor: rename remaining tests to NATS.Server.Core.Tests

- Rename tests/NATS.Server.Tests -> tests/NATS.Server.Core.Tests
- Update solution file, InternalsVisibleTo, and csproj references
- Remove JETSTREAM_INTEGRATION_MATRIX and NATS.NKeys from csproj (moved to JetStream.Tests and Auth.Tests)
- Update all namespaces from NATS.Server.Tests.* to NATS.Server.Core.Tests.*
- Replace private GetFreePort/ReadUntilAsync helpers with TestUtilities calls
- Fix stale namespace in Transport.Tests/NetworkingGoParityTests.cs

tests/NATS.Server.Core.Tests/Protocol/ProtocolParserSnippetGapParityTests.cs

@@ -0,0 +1,45 @@
+using System.Buffers;
+using System.Text;
+using NATS.Server.Protocol;
+
+namespace NATS.Server.Core.Tests.ProtocolParity;
+
+public class ProtocolParserSnippetGapParityTests
+{
+    [Fact]
+    public void ProtoSnippet_returns_empty_quotes_when_start_is_out_of_range()
+    {
+        var bytes = "PING"u8.ToArray();
+        var snippet = NatsParser.ProtoSnippet(bytes.Length, 2, bytes);
+        snippet.ShouldBe("\"\"");
+    }
+
+    [Fact]
+    public void ProtoSnippet_limits_to_requested_window_and_quotes_output()
+    {
+        var bytes = "ABCDEFGHIJ"u8.ToArray();
+        var snippet = NatsParser.ProtoSnippet(2, 4, bytes);
+        snippet.ShouldBe("\"CDEF\"");
+    }
+
+    [Fact]
+    public void ProtoSnippet_matches_go_behavior_when_max_runs_past_buffer_end()
+    {
+        var bytes = "ABCDE"u8.ToArray();
+        var snippet = NatsParser.ProtoSnippet(0, 32, bytes);
+        snippet.ShouldBe("\"ABCD\"");
+    }
+
+    [Fact]
+    public void Parse_exceeding_max_control_line_includes_snippet_context_in_error()
+    {
+        var parser = new NatsParser();
+        var longSubject = new string('a', NatsProtocol.MaxControlLineSize + 1);
+        var input = Encoding.ASCII.GetBytes($"PUB {longSubject} 0\r\n\r\n");
+        ReadOnlySequence<byte> buffer = new(input);
+
+        var ex = Should.Throw<ProtocolViolationException>(() => parser.TryParse(ref buffer, out _));
+        ex.Message.ShouldContain("Maximum control line exceeded");
+        ex.Message.ShouldContain("snip=");
+    }
+}