If a session is loaded that has an accept_port_types or reject_port_types
field, when the json file is de-serialized, what should be a set
internally becomes a list.

This commit ensures that the data in the model is always a set,
making conversion each time.

attr clean up and version bump.

this allows application code to construct an absolute
path to the shortcut menu json definition at runtime
(using importlib.resources or relative to __file__)
while the dynamically loaded python module path
('file' key) is assumed relative to the json path.
If an absolute filepath is given in the menu data dict,
that is used instead.

Makes the basic example much more robust, and able to run without
a specific cwd

Interpret function file path in menu data relative to menu json

fix: #425 ensure accept/reject port type is a set