Add async/await support to the JavaScript engine: - Add `Await` opcode (0x82) to bytecode format - Add `is_async` flag to bytecode Function struct - Compile async function declarations, expressions, arrows, and methods - Compile `await expr` to emit Await opcode - Parse `for await...of` syntax - VM creates internal generator for async functions, driven by promises - Await suspends generator and sets up promise reactions for resume - Rejected await throws into generator (preserving try/catch) - Save/restore exception handlers across yield/await suspension points - Async generators return async iterator wrappers - 16 unit tests covering all async patterns Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>