Allow replacing nodes

[liamhuber]

Composite instances can now replace one of their children with another node instance or class, as long as that node has no parent or connections and has compatible IO (this PR introduces a tool for coping connections from one node to the other)

Resolves a couple of the TODOs on #7.

from pyiron_workflow import Workflow

@Workflow.wrap_as.single_value_node()
def add_one(x):
    result = x + 1
    return result

@Workflow.wrap_as.macro_node()
def add_three_macro(macro):
    macro.one = add_one()
    macro.two = add_one(x=macro.one)
    macro.three = add_one(x=macro.two)
    
    macro.inputs_map = {"one__x": "x"}
    macro.outputs_map = {"three__result": "result"}

macro = add_three_macro()

replacement = add_three_macro()

print(macro(x=0).result)  # 1 + 1 + 1 = 3
>>> 3

macro.replace(macro.two, replacement)
# Alternate syntaxes support using labels and classes:
# macro.replace("two", replacement)
# macro.replace(macro.two, add_three_macro)
# macro.two.replace_with(replacement)
# macro.two.replace_with(add_three_macro)
# macro.two = add_three_macro  # Some real sugar!
print(macro(x=0).result)  # 1 + (1 + 1 + 1) + 1 = 5
>>> 5

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Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.58% (target: -1.00%)	92.59%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (d9aa842)	1580	1299	82.22%
Head commit (de0699a)	1627 (+47)	1347 (+48)	82.79% (+0.58%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#26)	54	50	92.59%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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