feat: Implement Phase 1 OMS with complete state machine

- Add OrderModels with all enums and records
- Implement IOrderManager interface
- Create BasicOrderManager with thread-safe state machine
- Add INT8OrderAdapter interface for NT8 integration
- Implement MockNT8OrderAdapter for testing
- Add comprehensive unit tests (34 tests, all passing)
- Full C# 5.0 compliance
- >95% code coverage
- Zero build warnings for new code

Closes Phase 1 OMS implementation

tests/NT8.Core.Tests/Mocks/MockLogger.cs

@@ -0,0 +1,34 @@
+using System;
+using Microsoft.Extensions.Logging;
+
+namespace NT8.Core.Tests.Mocks
+{
+    /// <summary>
+    /// Simple mock implementation of ILogger for testing purposes
+    /// </summary>
+    public class MockLogger<T> : ILogger<T>
+    {
+        public IDisposable BeginScope<TState>(TState state)
+        {
+            return new MockDisposable();
+        }
+
+        public bool IsEnabled(LogLevel logLevel)
+        {
+            return true;
+        }
+
+        public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
+        {
+            // Mock implementation - do nothing
+        }
+
+        private class MockDisposable : IDisposable
+        {
+            public void Dispose()
+            {
+                // Mock implementation - do nothing
+            }
+        }
+    }
+}