[janickm]

Summary

Small cleanup of the motion compensation and pose interpolation classes in ncore.geometry before the 20.0 freeze. The free functions (se3_inverse, transform_point_cloud, bbox_pose, ...) are unchanged.

Stack (merge from the top to land all six at once):

1. Keyword-only parameters and public exports
2. Storage contract and Group / Array API
3. Sensor models
4. Geometry cleanup (this PR)
5. Loaders, V4 components, and ValueError for user-facing validation
6. Converter default, wheel requirements, tools and docs (upgrading guide)

Changes

• MotionCompensator.motion_decompensate_points returns a MotionCompensator.MotionDecompensationResult (the decompensated points xyz_pointtime plus the reference frame, reference timestamp and anchor frame), mirroring motion_compensate_points. It is a separate type because the compensation result holds a start / end point pair, while decompensation yields one point set. Both result types are documented field by field. The in-repo converters read the points from the result.
• MotionCompensator(pose_graph, *, parameters), and reference_timestamp_us / anchor_frame_id of both (de)compensation methods are keyword-only, like the optional parameters of the other public APIs.
• PoseInterpolator takes typed array-like poses and timestamps (in_range too) and documents the time domain. Its scipy interpolants and homogeneous row are private (_slerp, _f_t, _last_row).
• An empty decompensation records the resolved reference timestamp (the frame end) instead of None.

Testing

• A test runs the converters' frame alignment with a real MotionCompensator, covering the converter-facing path (the dataset converter tests need datasets).
• Breaking a change on purpose makes its test fail: returning the bare array again (frame alignment and transformation tests), a public slerp (True is not false : slerp), recording the unresolved reference timestamp.
• bazel test //... --config=no-gpu green on all four interpreters, bazel build //... (ty), docs with warnings as errors, bazel run //:format.check clean.

Upgrading

• xyz = mc.motion_decompensate_points(...) -> xyz = mc.motion_decompensate_points(...).xyz_pointtime.
• MotionCompensator(pose_graph, params) -> MotionCompensator(pose_graph, parameters=params); pass reference_timestamp_us / anchor_frame_id by keyword.
• PoseInterpolator.slerp, f_t and last_row are private: use interpolate_to_timestamps / extrapolate_to_timestamps.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactoring (no functional changes)

Checklist

• I have read the Contributing Guidelines
• My commits follow Conventional Commits format
• My commits are GPG-signed
• I have added tests that prove my fix is effective or my feature works
• New and existing tests pass locally (bazel test //...)
• Code is formatted (bazel run //:format)
• I have updated documentation as needed
• My changes include SPDX license headers on all new files