feat: Nested states (compound / parallel) and support for SCXML (test suit)

[fgmacedo]

Another approach for #329.

By supporting the test cases defined at https://www.w3.org/Voice/2013/scxml-irp/ we can incorporate small functionalities until we get covered by the full spec.

[codecov]

Codecov Report

Attention: Patch coverage is 93.60269% with 114 lines in your changes missing coverage. Please review.

Project coverage is 96.21%. Comparing base (4449a9c) to head (93eaa58).

Files with missing lines	Patch %	Lines
statemachine/io/scxml/actions.py	92.12%	17 Missing and 9 partials ⚠️
statemachine/contrib/diagram.py	69.23%	11 Missing and 5 partials ⚠️
statemachine/io/scxml/parser.py	93.02%	7 Missing and 8 partials ⚠️
statemachine/engines/base.py	96.26%	5 Missing and 7 partials ⚠️
statemachine/orderedset.py	81.57%	7 Missing ⚠️
statemachine/engines/sync.py	92.30%	4 Missing and 1 partial ⚠️
statemachine/statemachine.py	92.75%	3 Missing and 2 partials ⚠️
statemachine/engines/async_.py	73.33%	3 Missing and 1 partial ⚠️
statemachine/factory.py	94.11%	2 Missing and 2 partials ⚠️
statemachine/io/scxml/processor.py	97.27%	0 Missing and 4 partials ⚠️
... and 9 more

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #501      +/-   ##
===========================================
- Coverage   100.00%   96.21%   -3.79%     
===========================================
  Files           25       31       +6     
  Lines         1631     3227    +1596     
  Branches       257      466     +209     
===========================================
+ Hits          1631     3105    +1474     
- Misses           0       71      +71     
- Partials         0       51      +51     

Flag	Coverage Δ
unittests	96.21% <93.60%> (-3.79%)	⬇️

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[sonarqubecloud]

Quality Gate failed

Failed conditions
4 Security Hotspots

See analysis details on SonarQube Cloud

[comalice]

Is this in a state (🤣) that I could try it out? I have several use-cases where the sub-state functionality would be useful and I'd be glad to give feedback if I run into issues.

Note, the user experience I had expected looked something like this:

class SubMachine(StateMachine):
    test = State(initial=True)
    test_complete = State(final=True)

    next = test.to(test_complete)


class TestSM(StateMachine):
    initial_state = State(initial=True)
    sub_machine_as_state = SubMachine()
    some_other_state = State(final=True)

    goto_sub_machine = initial_state.to(sub_machine_as_state)
    goto_finish = sub_machine_as_state.to(some_other_state)

And then something like

sm = TestSM()

sm.send('goto_sub_machine')
sm.send('next')   # TestSM now has the submachine states as states it can traverse.
sm.send('goto_finish')