I am trying to integrate RustPython into a game using Bevy and although I am able to find a solution using exclusive systems it is not very flexible and prevents other unrelated systems from running in parallel.

The core issue is that Sync is not currently implemented for VirtualMachine, or more precisely for the RefCell wrapping std::vec::Vec<PyRef<rustpython_vm::frame::Frame>>.

Is it possible to use a Mutex internally instead of a RefCell? Or if this is not desirable, perhaps just when RustPython's threading feature is enabled?