Fix 32-bit thread context API selection in DllInjector

Because DllInjector enforces matching host/target bitness, a 32-bit caller
always handles a 32-bit target. The correct API is native
GetThreadContext/SetThreadContext with Context32; the Wow64 APIs are only for
64-bit processes inspecting WOW64 targets, which never happens here.

- Collapse the 32-bit path to always use GetThreadContext/SetThreadContext.
- Remove the now-unused Wow64GetThreadContext/Wow64SetThreadContext
  declarations.
- Update Context32 doc comment to describe the x86 usage.
- ExternalReader access guard now also accepts QueryLimitedInformation.

Tests: 207 passing, 4 skipped.

WhiteMagic/Native/NativeMethods.cs

@@ -152,19 +152,6 @@ internal static partial class NativeMethods
         SafeMemoryHandle thread,
         ref Context32 context);
 
-    /// <summary>Sets a 32-bit (WOW64) thread context.</summary>
-    [LibraryImport("kernel32.dll", SetLastError = true)]
-    [return: MarshalAs(UnmanagedType.Bool)]
-    internal static partial bool Wow64SetThreadContext(
-        SafeMemoryHandle thread,
-        ref Context32 context);
-
-    /// <summary>Gets a 32-bit (WOW64) thread context.</summary>
-    [LibraryImport("kernel32.dll", SetLastError = true)]
-    [return: MarshalAs(UnmanagedType.Bool)]
-    internal static partial bool Wow64GetThreadContext(
-        SafeMemoryHandle thread,
-        ref Context32 context);
 
     // ── Modules ──────────────────────────────────────────────────────────────