feat: add StringReference.GetValue/GetRaw (Python parity) (#34)

Closes HIGH convenience gap #4. Python's StringReference exposes
.value (decoded text) and .raw (bytes) (binaryview.py:510/:514); the
C# StringReference is a handle-less Type/Start/Length carrier, so
callers had to separately ReadData(Start, Length) and hand-decode per
StringType.

Add durable GetValue(this StringReference, BinaryView) and
GetRaw(this StringReference, BinaryView) extension methods with a
StringType -> Encoding table mirroring Python's _decodings
(Ascii->ASCII, Utf8->UTF8, Utf16->Unicode/UTF-16LE, Utf32->UTF32LE).
GetValue decodes with .NET's default replacement fallback, the
equivalent of Python errors='replace'. The view is a parameter because
StringReference does not own one (unlike Python); extending its shape
would force a FromNative signature change threaded through the
TakeStructArray pipelines, so composition-only extensions are cleaner.

Author: tinysec

NavigationExtensions.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Runtime.InteropServices;
+using System.Text;
 
 namespace BinaryNinja
 {
@@ -635,6 +636,56 @@ public static bool Contains(this BinaryView view, ulong address)
             };
         }
 
+        // Maps each StringType to the .NET encoding Python's StringReference._decodings uses
+        // (binaryview.py:491): Ascii->ascii, Utf8->utf-8, Utf16->utf-16, Utf32->utf-32. UTF-16 LE
+        // is Encoding.Unicode and UTF-32 LE is Encoding.UTF32 on all platforms Binary Ninja runs on.
+        private static readonly Dictionary<StringType, Encoding> s_stringDecodings =
+            new Dictionary<StringType, Encoding>
+            {
+                { StringType.AsciiString, Encoding.ASCII },
+                { StringType.Utf8String, Encoding.UTF8 },
+                { StringType.Utf16String, Encoding.Unicode },
+                { StringType.Utf32String, Encoding.UTF32 },
+            };
+
+        /// <summary>
+        /// The raw bytes of this string reference, mirroring Python <c>StringReference.raw</c>
+        /// (binaryview.py:514): reads <see cref="StringReference.Length"/> bytes at
+        /// <see cref="StringReference.Start"/> from <paramref name="view"/>. The view is taken as a
+        /// parameter because <see cref="StringReference"/> is a handle-less value carrier and does
+        /// not own one (unlike Python, where the reference stores the view).
+        /// </summary>
+        public static byte[] GetRaw(this StringReference stringReference, BinaryView view)
+        {
+            if (null == view)
+            {
+                throw new ArgumentNullException(nameof(view));
+            }
+
+            return view.ReadData(stringReference.Start, stringReference.Length);
+        }
+
+        /// <summary>
+        /// The decoded text of this string reference, mirroring Python <c>StringReference.value</c>
+        /// (binaryview.py:510): reads the bytes via <see cref="GetRaw"/> and decodes them according
+        /// to <see cref="StringReference.Type"/>. Undecodable bytes are replaced rather than
+        /// thrown, matching Python <c>errors='replace'</c>.
+        /// </summary>
+        public static string GetValue(this StringReference stringReference, BinaryView view)
+        {
+            byte[] raw = GetRaw(stringReference, view);
+
+            // Fall back to ASCII for an unexpected StringType, matching Python's dict lookup
+            // semantics as closely as possible (Python would KeyError; the binding degrades
+            // gracefully because the type is an open enum).
+            s_stringDecodings.TryGetValue(stringReference.Type, out Encoding? foundEncoding);
+            Encoding encoding = foundEncoding ?? Encoding.ASCII;
+
+            // .NET's default decoders use replacement fallback (U+FFFD / '?'), which is the
+            // equivalent of Python errors='replace'.
+            return encoding.GetString(raw);
+        }
+
         /// <summary>
         /// Every disassembly instruction line across the whole view, in
         /// view-block-then-instruction order. Mirrors Python <c>BinaryView.instructions</c>