Add Closest Node(s) API method

[cadop]

A user should be able to query the closest node from a provided xyz position. The options could be:

• Get the closest node (by ID) to an Arbitrary xyz position
• Get the closest node (by ID) to another node (by ID)
• Get all nodes within a threshold
• Get nodes from a set of node IDs or arbitrary xyz positions
  • User provides a list of node ids or xyz pos, and an optional threshold value, they get back essentially an aggregated list of values like the functions above, for each of the input nodes.

Return options:

• list of node ids
• list of nodes (node type/struct)
• list of (node id, distance)