Weighting with list of 1d vectors

[kohr-h]

Between constant and "full array" weighting, there's weighting by an outer product of vectors that can be efficiently stored. Question: do we need this? It's a TODO in #861 anyway but won't be resolved there.

[adler-j]

Main use case would be the weighting with uniformly sampled ray-transform data, for example.

It may be worth it, depending on the effort needed.