mw_ APIs for SOECPotential and SOECPComponent

[camelto2]

Please review the developer documentation
on the wiki of this project that contains help and requirements.

Proposed changes

This PR add mw_ APIs for the SOECPotential and components, so now running in the batched code doesn't have to fall back to the single walker APIs. While designing the unit test, I also did a bit of refactoring in the potential and component classes. Also, a new standalone unit test was added similar to test_NonLocalECPotential.

part of #3712, finishes the last bullet point

What type(s) of changes does this code introduce?

Delete the items that do not apply

• New feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)

Does this introduce a breaking change?

• No

What systems has this change been tested on?

my M1 mac

Checklist

Update the following with a yes where the items apply. If you're unsure about any of them, don't hesitate to ask. This is
simply a reminder of what we are going to look for before merging your code.

• Yes. This PR is up to date with current the current state of 'develop'
• Yes. Code added or changed in the PR has been clang-formatted
• Yes. This PR adds tests to cover any new code, or to catch a bug that is being fixed
• No. Documentation has been added (if appropriate)

[ye-luo]

Please put all the variable names in lower case. IonNeighborElecs_-> ion_neighbor_elecs_ to be compliant with up-to-date naming convention.

[camelto2]

done

[ye-luo]

Test this please