Add memory-region query, enumeration, and scoped protection

Implements VirtualQueryEx + MEMORY_BASIC_INFORMATION wrappers, the immutable MemoryRegion record, the ProtectionScope disposable helper, and MemoryBase.QueryRegion/EnumerateRegions/ChangeProtection. Closes section 1 of add-thread-region-finder.

WhiteMagic/Memory/ProtectionScope.cs

@@ -0,0 +1,58 @@
+using System;
+using System.Runtime.InteropServices;
+using WhiteMagic.Native;
+
+namespace WhiteMagic.Memory;
+
+/// <summary>
+/// A scope that temporarily changes page protection via <c>VirtualProtectEx</c> and
+/// restores the original protection when disposed, including when the guarded body throws.
+/// </summary>
+public sealed class ProtectionScope : IDisposable
+{
+    private readonly MemoryBase _memory;
+    private readonly IntPtr _address;
+    private readonly nint _size;
+    private readonly MemoryProtectionType _originalProtection;
+    private bool _disposed;
+
+    /// <summary>
+    /// Creates a new protection scope, applying <paramref name="newProtection"/> to the
+    /// specified range immediately.
+    /// </summary>
+    internal ProtectionScope(MemoryBase memory, IntPtr address, nint size, MemoryProtectionType newProtection)
+    {
+        _memory = memory ?? throw new ArgumentNullException(nameof(memory));
+
+        if (address == IntPtr.Zero)
+            throw new ArgumentException("Address cannot be zero.", nameof(address));
+
+        if (size <= 0)
+            throw new ArgumentOutOfRangeException(nameof(size), "Size must be positive.");
+
+        _address = address;
+        _size = size;
+
+        if (!NativeMethods.VirtualProtectEx(
+                memory.Handle,
+                address,
+                size,
+                newProtection,
+                out _originalProtection))
+        {
+            int error = Marshal.GetLastPInvokeError();
+            throw new InvalidOperationException(
+                $"VirtualProtectEx failed to change protection: error {error}.");
+        }
+    }
+
+    /// <summary>Restores the original page protection if it has not already been restored.</summary>
+    public void Dispose()
+    {
+        if (!_disposed)
+        {
+            _disposed = true;
+            NativeMethods.VirtualProtectEx(_memory.Handle, _address, _size, _originalProtection, out _);
+        }
+    }
+}