feat!: add cooperative execution-time limits across engine, VM, and binding (#539)

- Introduce ExecutionTimer/ExecutionTimerConfig to allow limiting evaluating time.
- To amortize time checking costs, checking interval can be configured via the notion of work units
- A global fallback time limit can be set to universally limit all evaluation in addition to engine level limit setting.
- Implement limnits in interpreter and RVM. In RVM, also handle suspend/resume so that time during pause is not counted.
- Add engine-level APIs to set/clear per-engine timer configuration and apply global fallback defaults.
- Surface execution-time limits through FFI and C# bindings
- Add C# tests and example usage to validate engine overrides, global fallback behavior, and compiled policy enforcement.
- Expand docs for execution-time limit
- Add interpreter YAML cases and VM unit tests for time-limit behavior and deterministic time sources.

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

bindings/csharp/Regorus/Engine.cs

@@ -2,6 +2,8 @@
 // Licensed under the MIT License.
 
 using System;
+using System.Runtime.InteropServices;
+using System.Text;
 using Regorus.Internal;
 
 
@@ -24,6 +26,17 @@ namespace Regorus
             _handle = RegorusEngineHandle.Create();
         }
 
+        public static void SetFallbackExecutionTimerConfig(ExecutionTimerConfig config)
+        {
+            var nativeConfig = config.ToNative();
+            CheckAndDropResult(Regorus.Internal.API.regorus_set_fallback_execution_timer_config(nativeConfig));
+        }
+
+        public static void ClearFallbackExecutionTimerConfig()
+        {
+            CheckAndDropResult(Regorus.Internal.API.regorus_clear_fallback_execution_timer_config());
+        }
+
         public void Dispose()
         {
             Dispose(disposing: true);
@@ -87,6 +100,32 @@ namespace Regorus
                 }
             });
         }
+
+        public void SetExecutionTimerConfig(ExecutionTimerConfig config)
+        {
+            ThrowIfDisposed();
+            var nativeConfig = config.ToNative();
+            UseHandle(enginePtr =>
+            {
+                unsafe
+                {
+                    var localConfig = nativeConfig;
+                    CheckAndDropResult(Regorus.Internal.API.regorus_engine_set_execution_timer_config((Regorus.Internal.RegorusEngine*)enginePtr, &localConfig));
+                }
+            });
+        }
+
+        public void ClearExecutionTimerConfig()
+        {
+            ThrowIfDisposed();
+            UseHandle(enginePtr =>
+            {
+                unsafe
+                {
+                    CheckAndDropResult(Regorus.Internal.API.regorus_engine_clear_execution_timer_config((Regorus.Internal.RegorusEngine*)enginePtr));
+                }
+            });
+        }
         public string? AddPolicy(string path, string rego)
         {
             ThrowIfDisposed();
@@ -355,7 +394,21 @@ namespace Regorus
             });
         }
 
-        string? CheckAndDropResult(Regorus.Internal.RegorusResult result)
+    private static string? StringFromUtf8(IntPtr ptr)
+        {
+
+#if NETSTANDARD2_1
+			return Marshal.PtrToStringUTF8(ptr);
+#else
+            int len = 0;
+            while (Marshal.ReadByte(ptr, len) != 0) { ++len; }
+            byte[] buffer = new byte[len];
+            Marshal.Copy(ptr, buffer, 0, buffer.Length);
+            return Encoding.UTF8.GetString(buffer);
+#endif
+        }
+
+    private static string? CheckAndDropResult(Regorus.Internal.RegorusResult result)
         {
             try
             {