Geometry_Engine: Add IEndPoints methods to get end points from a curve

#### Description:

Current functionality requires you to use `IControlPoints` and sort order and take `.First()` and `.Last()`.

This should be updated in the Physical_Engine for `IsWithinPileCap` and `EmbedVolume` at the very least.

Start by locating the Geometry_Engine definitions of IEndPoints and IControlPoints, then inspect the Physical_Engine methods IsWithinPileCap and EmbedVolume that currently depend on sorted control points and First()/Last(). Done means endpoint access is available through IEndPoints and those two methods use it correctly, with relevant tests or validation run if present.

Written by the indexing model from the issue text.