Add coarse alignment and initial bias estimation utilities

[jbrodovsky]

Context

Strapdown performance is highly sensitive to initial attitude and bias estimates. A repeatable alignment step improves usability and reproducibility, especially for static start conditions.

Scope / Requirements

• Add an alignment helper to estimate roll/pitch from averaged accelerometer (gravity) over a configurable window.
• Optionally estimate yaw from magnetometer heading or GNSS course (when available).
• Estimate initial accel/gyro biases from the same static window.
• Expose alignment controls in strapdown-sim (e.g., --align-seconds, --align-use-mag, --align-use-gnss).
• Log alignment results and confidence indicators.

Acceptance Criteria

• On synthetic static data, alignment yields <1° roll/pitch error and <5° yaw error when a heading source is available.
• Output initial state matches InitialState conventions (degrees/radians, ENU/NED).
• Unit tests cover alignment against known vectors.