geometry: cuts stay on their plane; risky cuts are named (#384)

A partition intersects the body with a box on each side of the plane as
large as the body itself. SolidCraft's split_by_plane uses boxes several
times larger, and its boolean then put the cut up to 1.8 um off the plane
on the enclosure's air, so the cut faces were not recognized and the cells
did not close. A plane along a face of a body it cuts, or a cell whose
boundary does not tessellate into one a mesher takes (a cut through a
hole's axis), is a warning naming the partition, the body and where.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/tests/designs/pi5-enclosure.json

@@ -0,0 +1 @@
+[{"command": "solid.box", "params": {"length": 112, "width": 82, "height": 36, "corner": [0, 0, 0], "body_name": "Base"}}, {"command": "solid.fillet", "params": {"edges": [[0, 0, 18.0], [112, 0, 18.0], [0, 82, 18.0], [112, 82, 18.0]], "radius": 5}}, {"command": "solid.shell", "params": {"faces": [[56.0, 41.0, 36]], "thickness": 3, "direction": "inside", "body": "Base"}}, {"command": "solid.cylinder", "params": {"diameter": 13, "height": 36, "base": [-1, -1, 0], "operation": "join", "targets": ["Base"]}}, {"command": "solid.cylinder", "params": {"diameter": 13, "height": 36, "base": [113, -1, 0], "operation": "join", "targets": ["Base"]}}, {"command": "solid.cylinder", "params": {"diameter": 13, "height": 36, "base": [-1, 83, 0], "operation": "join", "targets": ["Base"]}}, {"command": "solid.cylinder", "params": {"diameter": 13, "height": 36, "base": [113, 83, 0], "operation": "join", "targets": ["Base"]}}, {"command": "solid.hole", "params": {"position": [-1, -1, 36], "diameter": 3.3, "depth": 20}}, {"command": "solid.hole", "params": {"position": [113, -1, 36], "diameter": 3.3, "depth": 20}}, {"command": "solid.hole", "params": {"position": [-1, 83, 36], "diameter": 3.3, "depth": 20}}, {"command": "solid.hole", "params": {"position": [113, 83, 36], "diameter": 3.3, "depth": 20}}, {"command": "solid.cylinder", "params": {"diameter": 6, "height": 6, "base": [16.5, 16.5, 3], "operation": "join", "targets": ["Base"]}}, {"command": "solid.cylinder", "params": {"diameter": 6, "height": 6, "base": [74.5, 16.5, 3], "operation": "join", "targets": ["Base"]}}, {"command": "solid.cylinder", "params": {"diameter": 6, "height": 6, "base": [16.5, 65.5, 3], "operation": "join", "targets": ["Base"]}}, {"command": "solid.cylinder", "params": {"diameter": 6, "height": 6, "base": [74.5, 65.5, 3], "operation": "join", "targets": ["Base"]}}, {"command": "sketch.create", "params": {"plane": {"origin": [0, 0, 0], "x_dir": [1, 0, 0], "y_dir": [0, 0, 1]}, "name": "Nut1"}}, {"command": 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"sketch.polygon.inscribed", "params": {"center": [66, 17], "radius": 11, "sides": 6, "angle": 0}}, {"command": "sketch.finish", "params": {}}, {"command": "solid.extrude", "params": {"sketch": "Nut2", "profiles": "all", "distance": 6, "operation": "new", "body_name": "Gland2"}}, {"command": "solid.cylinder", "params": {"diameter": 17, "height": 8, "base": [66, -6, 17], "axis": [0, -1, 0], "operation": "join", "targets": ["Gland2"]}}, {"command": "solid.cylinder", "params": {"diameter": 14, "height": 6, "base": [66, -14, 17], "axis": [0, -1, 0], "operation": "join", "targets": ["Gland2"]}}, {"command": "solid.fillet", "params": {"edges": [[66, -20, 24]], "radius": 2.5, "body": "Gland2"}}, {"command": "solid.cylinder", "params": {"diameter": 6.5, "height": 30, "base": [66, -20, 17], "axis": [0, -1, 0], "operation": "new", "body_name": "Cable2"}}, {"command": "sketch.create", "params": {"plane": {"origin": [112, 0, 0], "x_dir": [0, 1, 0], "y_dir": [0, 0, 1]}, "name": "Nut3"}}, {"command": "sketch.polygon.inscribed", "params": {"center": [41.0, 18], "radius": 14, "sides": 6, "angle": 0}}, {"command": "sketch.finish", "params": {}}, {"command": "solid.extrude", "params": {"sketch": "Nut3", "profiles": "all", "distance": 5, "operation": "new", "body_name": "Gland3"}}, {"command": "solid.cylinder", "params": {"diameter": 24, "height": 17, "base": [117, 41.0, 18], "axis": [1, 0, 0], "operation": "join", "targets": ["Gland3"]}}, {"command": "solid.hole", "params": {"position": [134, 41.0, 18], "diameter": 14, "depth": 15}}, {"command": "solid.fillet", "params": {"edges": [[134, 41.0, 30]], "radius": 2, "body": "Gland3"}}, {"command": "solid.box", "params": {"length": 110.8, "width": 80.8, "height": 1.6, "corner": [0.6, 0.6, 36], "operation": "new", "body_name": "ORing"}}, {"command": "solid.box", "params": {"length": 107.2, "width": 77.2, "height": 1.6, "corner": [2.4, 2.4, 36], "operation": "cut", "targets": ["ORing"]}}, {"command": "solid.box", "params": {"length": 128, "widthLine truncated