stations: place a curve or instance in the frame of an oriented curve station

[GeneralPawz]

A consumer needs a curve (or an instance) placed in the frame of an OrientedCurveStation on another curve: a local curve positioned at station s along a base, with the station's tangent/normal/binormal as its axes. One example is a segmented reference curve whose segments are placed by a linear placement.

Today:

• Instance takes only a resolved Transform3, so the consumer would have to evaluate the station itself and bake the frame. That loses exactness and the relation to the base.
• A station on an instance is refused (stations: basis on instances/relations, placement axis overrides, offset-curve end extension, tagged closed sections #246's known limit).

Needed

A graph relation that places a curve, or an instance, at an OrientedCurveStation. It keeps the reference symbolic and resolves the frame at evaluation with the same seam rule as other stations. It needs typed refusal when the frame is undefined (zero tangent, a seam with no selected side, a station out of range) and a deviation report when the frame is only certified rather than exact.

Done when

• The relation exists in the model and evaluates in reference.
• Tests cover: a line placed at a station on a straight base (exact); a placement at a station on an arc and on a banked or elevated base, checked against an independently evaluated frame; and refusal for out-of-range and degenerate stations.
• Stations on the placed curve itself work, or are refused with a typed error naming the remaining limit.

Consumer: openbimrs/ifc#311.