Refactor memory management into wibo::heap

- Removes blockUpper2GB hack; we now start early in the process
  and reserve all (available) space in the lower 2GB address
  space, leaving the upper 2GB untouched for host code
- All virtual memory operations flow through wibo::heap for
  bookkeeping
- All guest code uses a guest mimalloc area + thread-local heaps
  reserved in the guest address space

dll/kernel32/internal.h

@@ -157,7 +157,7 @@ struct HeapObject : public ObjectBase {
 	~HeapObject() override;
 
 	[[nodiscard]] inline bool isOwner() const { return pthread_equal(owner, pthread_self()); }
-	[[nodiscard]] inline bool canAccess() const { return (isProcessHeap || isOwner()) && heap != nullptr; }
+	[[nodiscard]] inline bool canAccess() const { return isProcessHeap || (isOwner() && heap != nullptr); }
 };
 
 inline constexpr uintptr_t kPseudoCurrentProcessHandleValue = static_cast<uintptr_t>(-1);