Fix LibraryLoader crash on error during context-transfer restoration

- Track whether transferred thread's original context was successfully restored.
- In the catch block, leak the remote allocation instead of freeing it if the thread was not restored; this prevents the target process from executing freed memory.
- Remove redundant 'op == 0x55' check in InstructionAnalyzer (already matched by (op & 0xF8) == 0x50).
- Simplify MemoryBase ReadString align-down expression to previousLen - (previousLen % nullLen).
- Change StubAllocator size parameter from nint to int for clarity (internal test seam).

Tests: 199 passing, 4 integration/interactive skipped.

WhiteMagic/MemoryBase.cs

@@ -211,8 +211,8 @@ public abstract class MemoryBase : IDisposable
             // Search the newly extended buffer at code-unit-aligned positions. A terminator
             // can start as far back as (nullLen - 1) bytes before the new bytes, so start
             // the search just before the previous end, rounded up to the next code-unit.
-            int firstAligned = ((previousLen - nullLen + 1 + nullLen - 1) / nullLen) * nullLen;
-            firstAligned = Math.Max(0, firstAligned);
+            int firstAligned = previousLen - (previousLen % nullLen);
+            if (firstAligned < 0) firstAligned = 0;
 
             int limit = accumulated.Count - nullLen;
             for (int i = firstAligned; i <= limit; i += nullLen)