[minor] Replace while with a macro pattern

[liamhuber]

The current while-loop metanode is (a) not a nice UI at all, and (b) not pickleable (or even easy to read/understand). I set out to replace it with something like the For class and for_node constructor for for-loops, but didn't find a way of breaking things out well enough to get a clean UI.

In lieu of replacing it with a new tool, here I just remove it entirely and replace it with a raw example (in both the deepdive and the integration tests) how you can make a cyclic subgraph directly as a macro. There is still some "universal" aspects to this that I'd love to eventually abstract out to a @as_while_loop decorator or something, but in the meantime I found sticking to a plain macro makes it much cleaner to handle setting up both the logic and the IO.

As long as body functionality and condition functionality are in turn nicely abstracted into their own nodes/macros, the example below is extremely generic. Note also that since the same nodes get executed multiple times, it also shows how the (new to this PR) AppendToList node can be used to track the parts of the history of the loop that is important to you.

from pyiron_workflow import Workflow

@Workflow.wrap.as_macro_node("greater")
def AddWhileLessThan(self, a, b, cap):
    """
    Add :param:`b` to :param:`a` while the sum is less than or equal to :param:`cap`.

    A simple but complete demonstrator for how to construct cyclic flows, including
    logging key outputs during the loop.
    """
    # Bespoke logic
    self.body = Workflow.create.standard.Add(obj=a, other=b)
    self.body.inputs.obj = self.body.outputs.add  # Higher priority connection
    # The output is NOT_DATA on the first pass and `a` gets used,
    # But after that the node will find and use its own output
    self.condition = Workflow.create.standard.LessThan(self.body, cap)

    # Universal logic
    self.switch = Workflow.create.standard.If(condition=self.condition)

    self.starting_nodes = [self.body]
    self.body >> self.condition >> self.switch
    self.switch.signals.output.true >> self.body

    # Bespoke logging
    self.history = Workflow.create.standard.AppendToList()
    self.history.inputs.existing = self.history
    self.history.inputs.new_element = self.body
    self.body >> self.history

    # Returns are pretty universal for single-value body nodes,
    # assuming a log of the history is not desired as output,
    # but in general return values are also bespoke
    return self.body

awlt = AddWhileLessThan()
out = awlt(0, 2, 5)

print(out)
>>> {'greater': 6}

print(awlt.history.outputs.list.value)
>>> [2, 4, 6]

awlt.draw(size=(10, 10))

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	Coverable lines	Covered lines	Coverage
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Head commit (2a8fa88)	3415 (-15)	3158 (-18)	92.47% (-0.12%)

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Pull Request Test Coverage Report for Build 9488435797

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• 0 of 0 changed or added relevant lines in 0 files are covered.
• 21 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.1%) to 92.477%

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Files with Coverage Reduction	New Missed Lines	%
create.py	9	92.16%
nodes/standard.py	12	91.72%

Totals
Change from base Build 9473872395:	-0.1%
Covered Lines:	3159
Relevant Lines:	3416

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Pull Request Test Coverage Report for Build 9488481429

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• 0 of 0 changed or added relevant lines in 0 files are covered.
• 21 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.1%) to 92.474%

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Files with Coverage Reduction	New Missed Lines	%
create.py	9	92.16%
nodes/standard.py	12	91.67%

Totals
Change from base Build 9473872395:	-0.1%
Covered Lines:	3158
Relevant Lines:	3415

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