chore: Example of issue #434

Author: fgmacedo

tests/testcases/issue434.md

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+### Issue 434
+
+A StateMachine that exercises the example given on issue
+#[434](https://github.com/fgmacedo/python-statemachine/issues/434).
+
+
+```py
+>>> from time import sleep
+>>> from statemachine import StateMachine, State
+
+>>> class Model:
+...     def __init__(self, data: dict):
+...         self.data = data
+
+>>> class DataCheckerMachine(StateMachine):
+...     check_data = State(initial=True)
+...     data_good = State(final=True)
+...     data_bad = State(final=True)
+...
+...     MAX_CYCLE_COUNT = 10
+...     cycle_count = 0
+...
+...     cycle = (
+...         check_data.to(data_good, cond="data_looks_good")
+...         | check_data.to(data_bad, cond="max_cycle_reached")
+...         | check_data.to.itself(internal=True)
+...     )
+...
+...     def data_looks_good(self):
+...         return self.model.data.get("value") > 10.0
+...
+...     def max_cycle_reached(self):
+...         return self.cycle_count > self.MAX_CYCLE_COUNT
+...
+...     def after_cycle(self, event: str, source: State, target: State):
+...         print(f'Running {event} {self.cycle_count} from {source!s} to {target!s}.')
+...         self.cycle_count += 1
+...
+
+```
+
+Run until we reach the max cycle without success:
+
+```py
+>>> data = {"value": 1}
+>>> sm1 = DataCheckerMachine(Model(data))
+>>> cycle_rate = 0.1
+>>> while not sm1.current_state.final:
+...     sm1.cycle()
+...     sleep(cycle_rate)
+Running cycle 0 from Check data to Check data.
+Running cycle 1 from Check data to Check data.
+Running cycle 2 from Check data to Check data.
+Running cycle 3 from Check data to Check data.
+Running cycle 4 from Check data to Check data.
+Running cycle 5 from Check data to Check data.
+Running cycle 6 from Check data to Check data.
+Running cycle 7 from Check data to Check data.
+Running cycle 8 from Check data to Check data.
+Running cycle 9 from Check data to Check data.
+Running cycle 10 from Check data to Check data.
+Running cycle 11 from Check data to Data bad.
+
+```
+
+
+Run simulating that the data turns good on the 5th iteration:
+
+```py
+>>> data = {"value": 1}
+>>> sm2 = DataCheckerMachine(Model(data))
+>>> cycle_rate = 0.1
+>>> while not sm2.current_state.final:
+...     sm2.cycle()
+...     if sm2.cycle_count == 5:
+...         print("Now data looks good!")
+...         data["value"] = 20
+...     sleep(cycle_rate)
+Running cycle 0 from Check data to Check data.
+Running cycle 1 from Check data to Check data.
+Running cycle 2 from Check data to Check data.
+Running cycle 3 from Check data to Check data.
+Running cycle 4 from Check data to Check data.
+Now data looks good!
+Running cycle 5 from Check data to Data good.
+
+```