Add back bench2.jl and rename it to bench_solve.jl

[ufechner7]

Add back the script bench2.jl to the test folder.

Reasons:

• benchmarking is hard
• you must avoid any changes to the code to achieve reproducible results
• you must always use the same hardware
• you must document the results over time

I think the allocations of solve! increased since I was running this script the last time, but I cannot be sure because the script was deleted. I documented the allocations in this script.

[1-Bart-1]

The comments are still there, but they are now in bench.jl:
https://github.com/Albatross-Kite-Transport/VortexStepMethod.jl/blob/e4c415768ccd6b01d9226e8092d5db12ab7664ff/test/bench.jl#L209C1-L215C34