MWE master-stepper

Create a MWE that does master-stepping as follows:

2. Run master stepper that initiates two steppers with arclength in both directions (positive and negative lambda) from a user-specified point with eigenvaluechange termination and load termination.
3. Master stepper identifies potential visiting of critical point twice within slave steppers.
4. Store the points where eigenvalue has changed.
5. Run dynamic solver from those points in both directions (speed or state perturbations along zero-stiffness modes).

No files, tests, or entry points are named in the issue. Start by locating the Python arc-length/master-stepper and dynamic-solver entry points; done means a runnable MWE covers the listed stepping, critical-point detection, point storage, and bidirectional dynamic runs.

Written by the indexing model from the issue text.