feat: make policy length limits configurable per engine (#624)

- Add PolicyLengthConfig struct with max_col, max_file_bytes, and
  max_lines fields, replacing hardcoded constants in the lexer.
- Add Engine::set_policy_length_config and clear_policy_length_config
  to allow callers to override the default limits.
- Add Source::from_contents_with_limits and from_file_with_limits for
  direct Source construction with custom limits; existing from_contents
  and from_file signatures are preserved using defaults.
- Add tests for default rejection, custom limits, and engine plumbing.
- Add bindings for C, C++, Python, WASM/JS, Java, Ruby, C#, Go

bindings/csharp/Regorus/NativeMethods.cs

@@ -428,6 +428,18 @@ namespace Regorus.Internal
         [DllImport(LibraryName, EntryPoint = "regorus_engine_clear_execution_timer_config", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
         internal static extern RegorusResult regorus_engine_clear_execution_timer_config(RegorusEngine* engine);
 
+        /// <summary>
+        /// Set the policy length limits for a specific engine instance.
+        /// </summary>
+        [DllImport(LibraryName, EntryPoint = "regorus_engine_set_policy_length_config", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
+        internal static extern RegorusResult regorus_engine_set_policy_length_config(RegorusEngine* engine, RegorusPolicyLengthConfig config);
+
+        /// <summary>
+        /// Clear the policy length configuration for a specific engine instance.
+        /// </summary>
+        [DllImport(LibraryName, EntryPoint = "regorus_engine_clear_policy_length_config", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
+        internal static extern RegorusResult regorus_engine_clear_policy_length_config(RegorusEngine* engine);
+
         #endregion
 
         #region Execution Timer Global Methods
@@ -772,6 +784,17 @@ namespace Regorus.Internal
         public uint check_interval;
     }
 
+    /// <summary>
+    /// FFI representation of the policy length configuration.
+    /// </summary>
+    [StructLayout(LayoutKind.Sequential)]
+    internal struct RegorusPolicyLengthConfig
+    {
+        public uint max_col;
+        public UIntPtr max_file_bytes;
+        public UIntPtr max_lines;
+    }
+
     /// <summary>
     /// Byte buffer returned from FFI.
     /// </summary>