Switch to pycolmap.Reconstruction for model converter. Add colmap visualizer with the same backend (Open3D)

[B1ueber2y]

Dependent on upstream #120

• Switch to pycolmap.Reconstruction from the deprecated namedcollections and remove PyReadCOLMAP
• Add some additional Python tests in the tests folder. Set up pytest and add it to CI. We should migrate the e2e test in the tests folder as well, but this will require merging the dataset implementation into the limap package.
• Add colmap visualizer with the same Open3D backend, to make the visualization consistent with the line maps. Also support robust ranges to prune outlier points.