Release v1.4.0

[petercorke]

Summary

Bumps the version to 1.4.0 and adds the [1.4.0] CHANGELOG.md section covering everything merged since v1.3.0 (59 commits): the Ellipsoid shape, Shape.corners()/bounds()/extents(), SceneNode.tree()/tree_children(), CollisionShapeGroup (with the & collision operator), Shape.opacity, Arrow.FromTo(), a cluster of Mesh improvements (y_up, the new mesh extra, read-only filename/y_up, an existence check at construction), the Path→Polyline rename, SceneNode's T=→pose= rename, update() becoming the real public method (replacing the misspelled _propogate_scene_tree()), the SceneGroup(initlist) fix, the Cylinder collision-length fix, and scene-graph cycle detection.

Compatibility note: everything here is backward-compatible via deprecated aliases (Path, _propogate_scene_tree()) except SceneNode.__init__'s T=→pose= rename, which has no back-compat shim — checked both robotics-toolbox-python and swift and neither uses the T= keyword anywhere, so this shouldn't affect real consumers.

See CHANGELOG.md's [1.4.0] entry for the full list.

Test plan

• CI on this PR (pytest matrix + docs build)

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