Integrate EKF-Based Initial Pose Estimation for NDT #757

Use previously available EKF pose estimates or predictions to initialize subsequent NDT scans in Awkernel. Establish a timestamp-aware feedback path without introducing circular waits between NDT and EKF processing.

Scope:

• Maintain a bounded history of EKF pose estimates with timestamps and validity information
• Select or derive an initial pose at the reference timestamp of each NDT scan
• Define permitted interpolation and prediction methods, including maximum time gaps and prediction horizons
• Apply the coordinate transforms required by the NDT initial-pose interface
• Define startup, stale-estimate, missing-history, and estimator-reset behavior
• Record which EKF estimates were used to initialize each scan

Acceptance criteria:

• Each NDT scan receives an initial pose corresponding to its reference timestamp within the defined temporal limits.
• Only EKF outputs available when the initial pose is selected are used; offline replay does not access outputs unavailable at the corresponding replay time.
• NDT does not wait for an EKF update that depends on the result of that same scan.
• Tests cover different NDT/EKF rates, delayed EKF outputs, missing history, excessive prediction horizons, and resets.
• Startup uses an explicitly supplied initial pose until valid EKF estimates become available.
• Invalid or stale estimates trigger the documented fallback or scan-rejection policy rather than being used silently.
• Selected source timestamps, interpolation or prediction intervals, and fallback decisions are logged for reproducibility.
• Integrated replay tests verify NDT convergence and localization error against predefined criteria.

Out of scope:

Changes to the NDT optimization algorithm or EKF state model, GNSS-based automatic initialization, and global relocalization.