Improve distance computation and add distance tool

[LionelZoubritzky-IGN]

Replace the previous distance helper implementation with a turf-based implementation.

Also add a distance tool to expose this primitive to the LLM for the specific case of point-to-point computation. This tool works with four different profiles:

• direct: distance as the crow flies (close Distance between two points tool #138).
• vincenty for high-precision ellipsoid distance.
• car and pedestrian: distances along an itinerary, computed with the Geoplateforme.

With the two latest mode, the time of travel is also returned. The itinerary can be chosen as the shortest time or the shortest distance.

Replaces #156 (updated algorithm and this PR is easier to maintain because it does not rely on my fork)

[LionelZoubritzky-IGN]

In the current state, all distance tests pass except a few edge cases where an ill-formed polygon circles around a pole. Those are marked as expected failures because I'm not sure it's really possible to do better without introducing a LOT of new code dedicated to the analysis of this special case... which does not seem worth it (the case of a well-formed polygon does work).

If you are curious though, there is a vibe-coded version in the https://github.com/ignfab/geocontext/tree/138/PROJECTIONS/distance-tool branch.