Speed up lookup table calculation

[aetherspritee]

• Rewrite main routine to use a single for loop
• Persist data after calculation and load it from file, since it only depends on lmax
• Overwrite persisted data if data for larger lmax is calculated, only load the required entries from it when using smaller lmax

[aetherspritee]

Loading and persisting data is working on 94fe587. I have a fortran script too, but i dont think its necessary given how lmax really doesnt ever need to change.

Will merge onto main in coming days

[arunoruto]

After merging #41 the tests are running without any issue.
The coverage report regarding the numerics file can be viewed here.

[arunoruto]

The commit 56074be shortens the for loops from 7 to 2 and introduces an additional flag for the computation to be forced, instead of loading the data from the cache.