Expose multi_stop_search on the .xrs DataArray accessor

[brendancol]

Description

xrspatial.multi_stop_search routes a least-cost path through a sequence of waypoints, but it is not reachable from the .xrs DataArray accessor. The # ---- Pathfinding ---- section of the accessor delegates only a_star_search. So raster.xrs.a_star_search(...) works, but raster.xrs.multi_stop_search(...) does not, and callers have to drop back to the module-level function.

Proposed solution

Add a multi_stop_search delegation method to XrsSpatialDataArrayAccessor, mirroring the existing a_star_search method. The first positional argument is waypoints; everything else forwards as keyword arguments.

raster.xrs.multi_stop_search(waypoints, optimize_order=True)

DataArray-only, matching a_star_search (the Dataset accessor does not expose pathfinding).

Scope

• Accessor delegation method under the Pathfinding banner.
• Presence and functional-parity test in test_accessor.py.
• Add multi_stop_search to the pathfinding reference docs, which currently list only a_star_search.

The multi_stop_search implementation does not change. It is already public and in the README feature matrix.