Add parser/compiler/runtime support for throw expressions, using and await using declarations, disposal stacks, dispose symbols, and SuppressedError handling. Wire disposal cleanup through blocks, returns, breaks, continues, and for-of loops, including async disposal paths and suppressed errors. Also add DisposableStack and AsyncDisposableStack builtins, AsyncIterator helper plumbing, and focused tests/spec coverage for resource management, suppression, throw expressions, and async iterators.