Add igl::boundary_conditions binding

[panangam]

Add binding code for igl::boundary_conditions and a test code for it.

[alecjacobson]

The test seems to be failing. Does it also fail on your end?

[alecjacobson]

Rebased onto current main and adjusted the test. The original test data (a single tet with bone/cage handles) made igl::boundary_conditions return false, so the wrapper's RuntimeError fired. The binding itself is correct; I replaced the test inputs with valid ones and added meaningful assertions:

• point handles at every vertex → bc is the identity;
• a bone edge with an interior sample vertex → all three bottom vertices become boundary samples of the single bone (weight 1).

Full suite green locally (92 passed). Thanks for the contribution!

(Written by Claude Code on behalf of @alecjacobson.)

[panangam]

Thank you for fixing that! BTW, this is Oras from your current SGI group :).

[alecjacobson]

@copilot resolve the merge conflicts in this pull request

[alecjacobson]

@copilot resolve the merge conflicts in this pull request