Let nodes run on instantiation

[liamhuber]

From #38

We won't abandon delayed execution, but let's add a flag to allow newly instantiated nodes to run (if ready), ala

from pyiron_workflow import Workflow

@Workflow.wrap_as.function_node(run_on_instantiation=True)
def update_immediately(x=0, y=1):
    return x+1, y+2

default_aggressive = update_immediately(y=3)
print(default_aggressive.outputs.to_value_dict())
>>> {"x+1": 1, "y+2": 5}

# Or
@Workflow.wrap_as.function_node()
def normal(x=0, y=1):
    return x-1, y-2

explicit_instruction_to_be_agressive = normal(x=10, run_on_instantiation=True)
print(explicit_instruction_to_be_agressive.outputs.to_value_dict())
>>> {"x-1": 9, "y-2": -1}