Path: Improve Detection of "Drillable" Holes

[jimzim111]

This PR includes two fixes to address valid/drillable holes not being included: an off-by-one list index when identifying potentially drillable cylinders, and incorrectly treating some through-holes as blind holes.

Detailed explanation and example screenshots are at https://forum.freecad.org/viewtopic.php?style=5&p=670298#p670298.

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[freecadci]

for feature branch PR_9038. Pipeline 817485875 was triggered at 61759ee. All CI branches and pipelines.

[sliptonic]

This seems to fail one of the unit tests.

======================================================================
FAIL: test20 (PathTests.TestPathDrillable.TestPathDrillable)
Test getDrillableTargets

Traceback (most recent call last):
File "/home/brad/FCD/FC/Mod/Path/PathTests/TestPathDrillable.py", line 269, in test20
self.assertEqual(len(results), 15)
AssertionError: 17 != 15

Please consider adding additional unit tests for the corner cases you're correcting. Thank you!

[luzpaz]

why was this PR closed ?

[jimzim111]

I mixed a couple of changes in this PR by accident, including one that's incomplete (and causes the test failure). So to avoid it becoming cluttered I closed this PR and opened #9146 with the one fix that's complete/ready, while I continue troubleshooting the other.