Enable deepcopy of bmb.Model

[lt-brs]

Hello !

I tried to deepcopy a bmb.Model and find out that we face a cannot pickle '_thread.lock' object.
After investigation, this is due to saving of thread locked objects within formulae.Environment objects.

Indeed many, locked variables are fetched while calling Environment.capture().
My dummy workaround was to just replace the return cls([frame.f_locals, frame.f_globals])

        if isinstance(env, cls):
            return env
        elif isinstance(env, numbers.Integral):
            depth = env + reference
        else:
            raise TypeError("'env' must be either an integer or an instance of Environment.")
        frame = inspect.currentframe()
        try:
            for _ in range(depth + 1):
                if frame is None:
                    raise ValueError("call-stack is not that deep!")
                frame = frame.f_back
            # return cls([frame.f_locals, frame.f_globals])
            return cls([])
        finally:
            del frame

I'm not experienced enough on Bambi formulae, a good workaround would be to keep only what is necessary for formulae to work in output of the capture() function

I hope it would be helpful

[tomicapretto]

Just want to say this seems to be related bambinos/bambi#400