fix(bindings): add SafeHandleWrapper + memory growth checks; bump 0.9.1 (#571)

- Introduce SafeHandleWrapper with gating, short drain wait, and deferred release on last in-flight exit.
- Wire Engine/Program/Rvm/CompiledPolicy to wrapper (centralized handle use, interop helper).
- Add C# memory growth tests (using/finalizer paths) and extend xtask C# runner options.
- Add pooled marshalling utilities, ResultHelpers, and API cleanups; update versions/changelog.

Fixes #570. Closes #554

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

bindings/csharp/Regorus/ModuleMarshalling.cs

@@ -0,0 +1,156 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+using System.Buffers;
+using System.Collections.Generic;
+using Regorus;
+
+#nullable enable
+
+namespace Regorus.Internal
+{
+    internal static unsafe class ModuleMarshalling
+    {
+        internal sealed class PinnedPolicyModules : IDisposable
+        {
+            private readonly List<Utf8Marshaller.PinnedUtf8> _pins;
+            private bool _disposed;
+
+            internal PinnedPolicyModules(RegorusPolicyModule[] buffer, int length, List<Utf8Marshaller.PinnedUtf8> pins)
+            {
+                Buffer = buffer;
+                Length = length;
+                _pins = pins;
+            }
+
+            internal RegorusPolicyModule[] Buffer { get; }
+
+            internal int Length { get; }
+
+            public void Dispose()
+            {
+                if (_disposed)
+                {
+                    return;
+                }
+
+                foreach (var pin in _pins)
+                {
+                    pin.Dispose();
+                }
+
+                ArrayPool<RegorusPolicyModule>.Shared.Return(Buffer, clearArray: true);
+                _disposed = true;
+            }
+        }
+
+        internal sealed class PinnedEntryPoints : IDisposable
+        {
+            private readonly List<Utf8Marshaller.PinnedUtf8> _pins;
+            private bool _disposed;
+
+            internal PinnedEntryPoints(IntPtr[] buffer, int length, List<Utf8Marshaller.PinnedUtf8> pins)
+            {
+                Buffer = buffer;
+                Length = length;
+                _pins = pins;
+            }
+
+            internal IntPtr[] Buffer { get; }
+
+            internal int Length { get; }
+
+            public void Dispose()
+            {
+                if (_disposed)
+                {
+                    return;
+                }
+
+                foreach (var pin in _pins)
+                {
+                    pin.Dispose();
+                }
+
+                ArrayPool<IntPtr>.Shared.Return(Buffer, clearArray: true);
+                _disposed = true;
+            }
+        }
+
+        internal static PinnedPolicyModules PinPolicyModules(IReadOnlyList<PolicyModule> modules)
+        {
+            if (modules is null)
+            {
+                throw new ArgumentNullException(nameof(modules));
+            }
+
+            var count = modules.Count;
+            var buffer = ArrayPool<RegorusPolicyModule>.Shared.Rent(count);
+            var pins = new List<Utf8Marshaller.PinnedUtf8>(count * 2);
+
+            try
+            {
+                for (int i = 0; i < count; i++)
+                {
+                    var idPinned = Utf8Marshaller.Pin(modules[i].Id);
+                    var contentPinned = Utf8Marshaller.Pin(modules[i].Content);
+                    pins.Add(idPinned);
+                    pins.Add(contentPinned);
+
+                    buffer[i] = new RegorusPolicyModule
+                    {
+                        id = idPinned.Pointer,
+                        content = contentPinned.Pointer
+                    };
+                }
+
+                return new PinnedPolicyModules(buffer, count, pins);
+            }
+            catch
+            {
+                foreach (var pin in pins)
+                {
+                    pin.Dispose();
+                }
+
+                ArrayPool<RegorusPolicyModule>.Shared.Return(buffer, clearArray: true);
+                throw;
+            }
+        }
+
+        internal static PinnedEntryPoints PinEntryPoints(IReadOnlyList<string> entryPoints)
+        {
+            if (entryPoints is null)
+            {
+                throw new ArgumentNullException(nameof(entryPoints));
+            }
+
+            var count = entryPoints.Count;
+            var buffer = ArrayPool<IntPtr>.Shared.Rent(count);
+            var pins = new List<Utf8Marshaller.PinnedUtf8>(count);
+
+            try
+            {
+                for (int i = 0; i < count; i++)
+                {
+                    var entryPinned = Utf8Marshaller.Pin(entryPoints[i]);
+                    pins.Add(entryPinned);
+                    buffer[i] = (IntPtr)entryPinned.Pointer;
+                }
+
+                return new PinnedEntryPoints(buffer, count, pins);
+            }
+            catch
+            {
+                foreach (var pin in pins)
+                {
+                    pin.Dispose();
+                }
+
+                ArrayPool<IntPtr>.Shared.Return(buffer, clearArray: true);
+                throw;
+            }
+        }
+    }
+}