Preprocessor fixes

[dvbuntu]

This PR fixes some of the logic with the Python preprocessing.py. Previously it looked for both maximum and minimum constraint violations, but based on this issue, I don't think we can actually check the minimum constraint this way.

Another fix is ignoring the Source and Sink nodes when checking for violating nodes. Previously we might have hit them early and missed violating nodes.

I also changed which node get identified as offending. Given a shortest resource path from Source to A, if the cost is say 10 while our maximum allowed is 5, then A cannot possibly be on the shortest resource-constrained path from Source to Sink. So we mark node A for removal. Previously, the predecessor to node A was removed, think under logic that the final edge (i.e. B-A) was the problem. But that could remove a node needed for other paths (see Issue #72 ). Node identified changed from -2 to -1.

Finally, if the shortest path from Source to A consumes too many resources (i.e. node becomes a key in nodes_source), that is sufficient to remove that node. Whether it also consumes too many from A to Sink becomes irrelevant (and vice versa) as it cannot be part of the shortest path. If my logic is mixed up, I'd be happy to revert the changes I made. node in nodes_source and nodes_sink changed to node in nodes_source or node in nodes_sink (note typo fix as well, was missing checking node in nodes_sink).

[sourcery-ai[bot]]

Sourcery Code Quality Report

✅  Merging this PR will increase code quality in the affected files by 0.49%.

Quality metrics	Before	After	Change
Complexity	5.88 ⭐	5.34 ⭐	-0.54 👍
Method Length	78.10 🙂	78.36 🙂	0.26 👎
Working memory	10.00 😞	9.74 🙂	-0.26 👍
Quality	59.38% 🙂	59.87% 🙂	0.49% 👍

Other metrics	Before	After	Change
Lines	205	226	21

Changed files	Quality Before	Quality After	Quality Change
src/python/preprocessing.py	51.64% 🙂	51.91% 🙂	0.27% 👍
test/python/tests_preprocessing.py	69.95% 🙂	68.59% 🙂	-1.36% 👎

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
src/python/preprocessing.py	prune_graph	16 🙂	247 ⛔	13 😞	35.36% 😞	Try splitting into smaller methods. Extract out complex expressions
src/python/preprocessing.py	prune_graph._check_resource	3 ⭐	109 🙂	13 😞	59.60% 🙂	Extract out complex expressions
test/python/tests_preprocessing.py	TestsPreprocessing.setUp	0 ⭐	239 ⛔	8 🙂	60.13% 🙂	Try splitting into smaller methods
test/python/tests_preprocessing.py	TestsPreprocessing.testFormatting	0 ⭐	125 😞	9 🙂	67.82% 🙂	Try splitting into smaller methods

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