Merging and splitting beams, node point precision and vector utility functions

[haavahk]

Changes are related to:

• typing and type hints, tying to make code consistent using from __future__ import annotations.

Additions are related to:

• merging beams
• splitting beam into two beams
• vector functions related to merging and splitting beams
• rounding of point precision on node
• safe adding/removing of objects to/from Node.refs

[Krande]

after skimming through your PR and tested this locally and found that all tests are passing. I have no issues accepting this :)

Thanks a lot!

Best Regards
Kristoffer

[Krande]

nice! I did not know about this. I am all for removing the " from any typechecked references :)