open3d tests exist but have presumably always been skipped in CI

[petercorke]

tests/test_pointcloud.py (TestPointCloud) and tests/test_ros.py both have real,
properly-guarded open3d tests (try: import open3d ... except ImportError: open3d_available = False + @unittest.skipUnless(open3d_available, "open3d not installed") in
test_pointcloud.py; an equivalent _open3d_importable flag pattern in test_ros.py). But
open3d has never been part of .github/workflows/ci.yml's installed package set, so these
tests have presumably always been silently skipped in CI — a pre-existing coverage gap, not a
regression from any recent change.

open3d is a real, major dependency (declared as its own optional extra,
open3d = ["open3d-python"], in pyproject.toml — note that PyPI name is itself stale/wrong,
the real maintained package is just open3d), but it chronically lags behind current Python
releases, so it can't be installed unconditionally across the repo's 3.10-3.13 test matrix.

Fix

Install open3d on whichever Python versions it actually currently supports and add it to CI
for just those legs (a CI-plumbing addition, not a code change) — check its current supported
Python range before picking a matrix subset. Fix the stale open3d-python PyPI name in
pyproject.toml's open3d extra at the same time.