Move O(n) operations to the initializer in exact_geodesics

[yutanoma]

Fixed exact_geodesics so that you do not need to run O(n) operations whenever you query the geodesic path.
This is especially useful when you have a fixed mesh/geometry and want to query the geodesic path multiple times.

Summary of contribution

• Moved geom.requireCornerAngles() and geom.requireVertexGaussianCurvatures() to the initializer
• Added clear_data() that clears the data except the ones associated with the mesh/geometry

Usage

std::vector<SurfacePoint> p0s, p1s;
// initialize your p0s/p1s here

GeodesicAlgorithmExact mmp(mesh, geometry);

for (int i = 0; i < p0s.size(); i++) {
  auto p0 = p0s[i];
  auto p1 = p1s[i];

  mmp.propagate({p0}, GEODESIC_INF, {p1});
  std::vector<SurfacePoint> path = mmp.traceBack(p1);
  // do science with your path here

  // clear the propagated data so that you can use `mmp` for another geodesic computation
  mmp.clear_data();
}

[nmwsharp]

Hey, looks like I forgot to merge this from ages ago -- my apologies!

Looking at it now, I have a question, it's not clear to me what clear() vs the new clear_data() do? Do you remember? I want to add some guidance for the user about when to call one vs. the other.

Is it that clear_data() needs to be called when propagating from a different source set? I'm a bit confused because it seems like clear() is already called at beginning of each propagate() and resets a bunch of data.