Add a `verb` string parameter to the `runFiber` helper function so that `Fiber.try()` produces consistent error messages like "Cannot try a finished fiber." instead of the previous generic fallback. Update all call sites (`fiber_call`, `fiber_call1`, `fiber_transfer`, `fiber_transfer1`) to pass the appropriate verb string, and add a new test case `try_error.wren` verifying the error message for trying an aborted fiber.