feat(ffi): unwind safety: shield FFI entrypoints with panic guard (#546)

This PR implements widely accepted Rust programming practices for
dealing with panics across ABI (programming language) boundaries.

- Add panic_guard.rs to wrap FFI calls and prevent panic across FFI/ABI boundary (undefined behavior).
- Capture per-thread backtraces via a temporary panic hook
- After a panic, subsequent invocations are poisoned.
- Integrate with_unwind_guard across the engine, schema registry, and target registry exportis

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

bindings/csharp/Regorus/StatusExtensions.cs

@@ -0,0 +1,24 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+
+#nullable enable
+
+namespace Regorus.Internal
+{
+    internal static class StatusExtensions
+    {
+        internal static Exception CreateException(this RegorusStatus status, string? message)
+        {
+            var details = string.IsNullOrWhiteSpace(message) ? "Regorus call failed." : message;
+
+            return status switch
+            {
+                RegorusStatus.Panic => new InvalidOperationException($"Regorus engine panicked: {details}"),
+                RegorusStatus.Poisoned => new InvalidOperationException($"Regorus engine is poisoned: {details}"),
+                _ => new Exception(details),
+            };
+        }
+    }
+}