Switch between small cones and big cones strategy in from_cones

[ManonMarchand]

We should think about a strategy to switch between the two algos.

@hombit benchmarked the small cone strategy (from MOC-cli) to be 7x faster for some use cases

TODO before: benchmark with systematic number of cells per cone variations at different depths to determine optimal switch points

[fxpineau]

@ManonMarchand (cc @hombit),
I just added a from_small_cones method (returning a single MOC) in the Rust wrapper.
See commit 8ddb6eb.

[fxpineau]

(Note that I added a multi-threaded version of from_small_cones, to be tested, in moc-lib-rust. See this commit)

[ManonMarchand]

Will be more complete with #174
We decided that switching automatically would be clumsy, so the choice is for the user. There is a new keyword in from_cones and in from_boxes that allows to chose between small and large strategy. The small one will usually be faster if the shapes don't overlap.

[hombit]

Sounds great, thank you so much!