fix(io): materialize transition validators from dict definitions

[csentis]

What

create_machine_class_from_definition builds each Transition with cond, unless, on, before, and after from the definition — but dropped validators. So a validators entry in a dict/JSON definition was silently ignored and never ran at send(). The TransitionDict TypedDict also mistyped validators as bool.

This PR:

• threads validators through to Transition(...) in create_machine_class_from_definition;
• corrects the TransitionDict.validators annotation to the same callback-spec union as cond/unless;
• adds a regression test (tests/test_io.py::TestTransitionValidators) proving a definition-supplied validator runs and aborts on send() (the test fails without the production change).

Why

Transition.__init__ already accepts validators=; only the dict adapter wasn't passing it. Validators are the documented explicit-rejection channel (raise with a reason) — without this, dict/JSON-defined machines can't use it.

Notes

• Two-line production change + type fix; no behavior change for definitions that don't set validators.
• ruff check clean; pytest tests/test_io.py green (4 passed).

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud