Revert rectangle generator to original spiral pattern for reimplementation

[Copilot]

The previous zig-zag rectangle construction implementation produced incorrect cell positions. The reviewer provided the correct expected zig-zag traversal order:

0→(0,0), 1→(1,0), 2→(1,1), 3→(0,1), 4→(0,2), 5→(1,2),
6→(2,2), 7→(2,1), 8→(2,0), 9→(3,0), 10→(3,1), ...

This commit reverts CudaShapeGenerator.cuh and ShapeGenerator.cpp back to the original spiral pattern. The correct zig-zag angle sequence has been derived (alternating ±90° turns with straight segments) but is not yet implemented.

Status: incomplete. The correct algorithm still needs to be implemented in a follow-up.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[chrxh]

@copilot your changes are wrong.
In the old rectangle construction (spiral pattern) the constructed cells had the positions (y- coordinates should be mirrored):

0 → (0, 0)
1 → (0, 1)
2 → (1, 1)
3 → (1, 0)
4 → (1, -1)
5 → (0, -1)
6 → (-1, -1)
7 → (-1, 0)
8 → (-1, 1)
9 → (-1, 2)
10 → (0, 2)
....

With the new zig-zag construction it should be:
0 → (0, 0)
1 → (1, 0)
2 → (1, 1)
3 → (0, 1)
4 → (0, 2)
5 → (1, 2)
6 → (2, 2)
7 → (2, 1)
8 → (2, 0)
9 → (3, 0)
10 → (3, 1)

[chrxh]

@copilot continue