Refactor torsiondrive for easy parallel subclass

[jthorton]

Description

This PR refactors the running of the optimizations for the torsiondrive procedure into a function that can be easily overridden by users who would like to implement a parallel version. This avoids users having to deal with the inner workings of the torsiondrives and can instead focus on the distribution of the optimization tasks.

Changelog description

The torsiondrive procedure has been refactored to make it easier for users to implement a parallel version via subclassing and overwriting the _spawn_optimizations method.

cc @SimonBoothroyd

Status

• Code base linted
• Ready to go

[codecov]

Codecov Report

Merging #351 (f794a53) into master (aeead6f) will increase coverage by 0.00%.
The diff coverage is 87.50%.

[dotsdl]

Looks great to me @jthorton! Thank you for putting this together!

[dotsdl]

@loriab it looks like Python 3.6 for xtB is blocking us here? Where is the CI running? Does it not exist anymore and need to be removed from required checks?

[loriab]

I remember seemingly removing xtb 3.6 a couple times and GH not being convinced. go ahead and merge when ready, and I'll take another look at required checks tomorrow.

[dotsdl]

Thanks @loriab! Unfortunately I don't have sufficient permissions on this repo to merge without that check. I can't click the merge button. 😢

[loriab]

Thanks @loriab! Unfortunately I don't have sufficient permissions on this repo to merge without that check. I can't click the merge button. 😢

See if merge clear now, @dotsdl

[dotsdl]

It works! Thanks @loriab!