fix: Multiple observers can watch the same callback

[fgmacedo]

Fixes #384 .

Multiple observers now can watch the same callback

we register multiple observers to the same named callback.

This works also as a regression test.

>>> from statemachine import State
>>> from statemachine import StateMachine

>>> class MyObs:
...     def on_move_car(self):
...         print("I observed moving from 1")

>>> class MyObs2:
...     def on_move_car(self):
...         print("I observed moving from 2")
...


>>> class Car(StateMachine):
...     stopped = State(initial=True)
...     moving = State()
...
...     move_car = stopped.to(moving)
...     stop_car = moving.to(stopped)
...
...     def on_move_car(self):
...         print("I'm moving")

Running:

>>> car = Car()
>>> obs = MyObs()
>>> obs2 = MyObs2()
>>> car.add_observer(obs)
Car(model=Model(state=stopped), state_field='state', current_state='stopped')

>>> car.add_observer(obs2)
Car(model=Model(state=stopped), state_field='state', current_state='stopped')

>>> car.add_observer(obs2)  # test to not register duplicated observer callbacks
Car(model=Model(state=stopped), state_field='state', current_state='stopped')

>>> car.move_car()
I'm moving
I observed moving from 1
I observed moving from 2
[None, None, None]

[sonarqubecloud]

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0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (c60f7fe) 100.00% compared to head (c22dcda) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop      #387   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           20        20           
  Lines          976       985    +9     
  Branches       161       163    +2     
=========================================
+ Hits           976       985    +9     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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Impacted Files	Coverage Δ
statemachine/callbacks.py	100.00% <100.00%> (ø)
statemachine/dispatcher.py	100.00% <100.00%> (ø)

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[fgmacedo]

author's note: Refac extracting methods from ensure_callable