[Feature Request] Aggreggation queries to subset of nodes

[chourmo]

I would be interested in limiting net.aggregate or net.nearest_pois queries to a subset of nodes to make them faster.

This would be useful to avoid nodes :

• on rural roads, with no population
• on highways with no direct local access
• to sample nodes in dense areas (city centers), with small differences in local accessibility
• avoid graph edges for which accessibility may have no meaning (transit, water ways (...))
• ....

API wise, a subset keyword with a list of nodes in net.aggregate and net.nearest_pois would be great.