Add benchmark for depth

[kushalpokharel]

This PR adds benchmarking for the depth function.

• Loads different numbers of points to the Rtree using the fold_left with a maximum load size of 3
• Runs the depth function in the loaded R-tree.

The thought behind assigning the maximum load size to 3 is to make the tree longer. Need feedback for this

[patricoferris]

Thanks @kushalpokharel this looks great, I pushed two extra commits one to format the code with dune build @fmt --auto and the second to run the benchmarks on my machine 👍