fix 7 correctness and cleanup issues

Blocking fixes:
1. Read<T> now returns default(T) on failed/partial read instead of crash
   (applies to single Read<T>, array Read<T>, and ReadBytes)
2. InProcessReader uses ReadProcessMemory via handle instead of unsafe
   Buffer.MemoryCopy — fails soft on bad address instead of AV'ing
3. GetRelative now returns absolute - ImageBase (inverse of GetAbsolute).
   Fix round-trip test to validate at arbitrary offsets, not just ImageBase
4. ReadString reads in 64-byte chunks with encoding-aware null-terminator
   pattern matching (handles UTF-16's 2-byte null, UTF-32's 4-byte null)

Cleanup:
5. InProcessReader validates handle on open and uses RPM through it
   (handle is no longer unused)
6. Array marshal read: pin raw buffer once, PtrToStructure at offset
7. StructureToByteArray(Span) delegates to byte[] overload, no duplicate

New tests: 4 invalid-address grace tests (returns default/empty/false).
All 57 passing.

WhiteMagicTest/AddressingTests.cs

@@ -7,6 +7,8 @@ namespace WhiteMagicTest;
 
 /// <summary>
 /// Tests for relative/absolute addressing in <see cref="MemoryBase"/>.
+/// GetAbsolute(relative) = ImageBase + relative.
+/// GetRelative(absolute) = absolute - ImageBase (inverse of GetAbsolute).
 /// </summary>
 public class AddressingTests
 {
@@ -27,31 +29,45 @@ public class AddressingTests
     }
 
     [Fact]
-    public void GetRelative_computes_offset_from_image_base()
+    public void GetRelative_returns_absolute_minus_image_base()
     {
         using var reader = OpenSelf();
         IntPtr imageBase = reader.ImageBase;
         IntPtr absolute = imageBase + 0x2000;
         IntPtr relative = reader.GetRelative(absolute);
-        // GetRelative returns ImageBase - absolute (GreyMagic convention)
-        Assert.Equal((IntPtr)((int)imageBase - (int)absolute), relative);
+        Assert.Equal((IntPtr)((nint)absolute - (nint)imageBase), relative);
     }
 
     [Fact]
-    public void GetAbsolute_after_GetRelative_at_image_base_returns_to_base()
+    public void GetAbsolute_and_GetRelative_are_inverses()
     {
         using var reader = OpenSelf();
-        IntPtr atBase = reader.ImageBase;
-        IntPtr relative = reader.GetRelative(atBase);
-        IntPtr back = reader.GetAbsolute(relative);
-        Assert.Equal(atBase, back);
+        IntPtr offset = (IntPtr)0x3000;
+
+        // Round-trip: offset -> absolute -> back to offset
+        IntPtr absolute = reader.GetAbsolute(offset);
+        IntPtr back = reader.GetRelative(absolute);
+        Assert.Equal(offset, back);
+
+        // Reverse round-trip: absolute -> offset -> back to absolute
+        IntPtr relative = reader.GetRelative(absolute);
+        IntPtr absoluteAgain = reader.GetAbsolute(relative);
+        Assert.Equal(absolute, absoluteAgain);
+    }
+
+    [Fact]
+    public void GetRelative_on_ImageBase_returns_zero()
+    {
+        using var reader = OpenSelf();
+        IntPtr relative = reader.GetRelative(reader.ImageBase);
+        Assert.Equal(IntPtr.Zero, relative);
     }
 
     [Fact]
     public void Read_with_isRelative_true_uses_image_base()
     {
         using var reader = OpenSelf();
-        // Read the first byte at ImageBase (should be MZ header: 0x4D = 'M')
+        // DOS header 'MZ' at the image base
         byte firstByte = reader.Read<byte>(IntPtr.Zero, isRelative: true);
         Assert.Equal(0x4D, firstByte);
     }
@@ -65,10 +81,9 @@ public class AddressingTests
         try
         {
             IntPtr absolute = pin.AddrOfPinnedObject();
-            nint relative = (nint)absolute - (nint)reader.ImageBase;
-            IntPtr relativePtr = (IntPtr)relative;
+            IntPtr relative = reader.GetRelative(absolute);
 
-            Assert.True(reader.Write(relativePtr, 42, isRelative: true));
+            Assert.True(reader.Write(relative, 42, isRelative: true));
             Assert.Equal(42, reader.Read<int>(absolute));
         }
         finally
@@ -81,7 +96,6 @@ public class AddressingTests
     public void ReadBytes_with_isRelative_true_resolves_correctly()
     {
         using var reader = OpenSelf();
-        // DOS header 'MZ' at the image base
         byte[] data = reader.ReadBytes(IntPtr.Zero, 2, isRelative: true);
         Assert.Equal(0x4D, data[0]);
         Assert.Equal(0x5A, data[1]);