Geometry nodes - Make structure creation and caching evident

Nodes like raycast and a few others use a BVHTree under the hood to do raycasts, or nearest element searches.

creation of these trees is done without hinting that it is happening - creation and use of these trees should be separated in a manner that one tree can be used in multiple nodes -

1. so each node does not need to create a new tree
2. so we have the opportunity to slap a 'cache' node on the bvhtree data stream and store it and use it over and over on things that don't change.

example - a scene where it is raining or snowing and we need to detect collisions with buildings and the ground

each frame every raycast node right now will build a new bvhtree and never re-use it.

this should allow some scenes to be about 20-100x faster.

New nodes - geometry to bvhtree and geometry to kdtree nodes - would then plug into new sockets added to nodes like raycast etc. these new 'streams' of data could get their own cache node.