Added a support to initialize apysc data types before a stage creation (v3.3.3)

[simon-ritchie]

Before version 3.3.3, the apysc library raises an exception when apysc data types are initialized before a stage creation.

For example, the following code had been raised before version 3.3.3, but now it can use with no exception.

import apysc as ap

MY_INT: ap.Int = ap.Int(10)
ap.Stage(
    stage_width=100, stage_height=50, background_color="#333", stage_elem_id="stage"
)

This support helps to define constants at the top-level scope.