fix(mobile): make PurePursuit usable; rst docstrings and shaped types in drivers.py

[petercorke]

What

PurePursuit in mobile/drivers.py could not run at all. This PR fixes it, and brings the whole file up to the project's docstring and typing standard.

Bugs fixed (problem-list entries 1-3)

• PurePursuit.demand() read self._waypoint_marker, which was never assigned: AttributeError on the first call.
• PurePursuit.init(ax) crashed with the default linemarkerstyle=None.
• PurePursuit.__str__ crashed when there was no workspace.
• __str__ of both drivers printed the x range as the y range.

Design

• The base class owns a single goal marker, created by _init_goal_marker() and moved by driveto() on every cycle, so RandomPath and PurePursuit share code and style. It moves; it does not leave a trail.
• PurePursuit draws its path as one line, styled by the new path_style argument (default: the look used in the book figures). linemarkerstyle never worked, so nothing can depend on it and it is replaced without an alias. No per-waypoint markers, because a path from a trajectory generator is dense.
• path is converted to a float 2xN array and validated (ValueError otherwise). A comment notes this belongs in spatialmath's getmatrix(): getmatrix() rejects a list of lists; revisit the base.X matrix/vector converters rai-opensource/spatialmath-python#255.

Naming and deprecation

• Style dicts are <thing>_style: goal_style (base class) and path_style (PurePursuit). goalmarkerstyle is deprecated: it still works, warns with DeprecationWarning and maps to goal_style.
• The defaults are module constants GOAL_STYLE and PATH_STYLE; a user dict is merged over them (DEFAULT | user, the user's values win).
• The same convention for the rest of mobile is a separate change.

Typing and docstrings

• Arguments and returns use spatialmath's Points2, ArrayLike2 and R2, since the names tell the reader what the shape is.
• All docstrings are reST; the leftover MATLAB-style docstring and comments are gone; :type: is kept only where shape adds information.

Testing

• Five new tests in DriversTest (path validation, __str__, a run without animation, the moving goal marker, the RandomPath goal marker). Four of them fail on main and pass here; the RandomPath marker test passes on both and guards the refactor.
• mypy clean (163 files).

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 13 complexity · 0 duplication

Metric	Results
Complexity	13
Duplication	0

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (f28437f) to head (9feaa7e).

Files with missing lines	Patch %	Lines
src/roboticstoolbox/mobile/drivers.py	0.00%	29 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #772   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files        143     143           
  Lines      14667   14667           
=====================================
  Misses     14667   14667           

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