Add one dim cubic spline with linear grid

[ye-luo]

Proposed changes

To be used in short range Coulomb PBC AA.

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

• New feature

Does this introduce a breaking change?

• No

What systems has this change been tested on?

epyc-server

Checklist

• 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
• Ye. This PR adds tests to cover any new code, or to catch a bug that is being fixed

[ye-luo]

Test this please

[prckent]

1. Why is this needed?
2. Add comments/definitions
3. Class not struct?
4. Private not public
5. Hopefully 100% test coverage

[ye-luo]

1. Why is this needed?

class containing pointers with virtual function pointer calls. I'd like to stay away from them inside a GPU kernel.

2. Add comments/definitions

I will add more.

3. 4. Private not public

Will do

5. Hopefully 100% test coverage

I hope so.

[ye-luo]

It is 90.90% unfortunately not 100%.

[prckent]

Good try on the coverage. Can you put a note about avoiding virtual functions for future people using/modifying this?

[ye-luo]

I added a note explaining that this class was made to avoid virtual functions on GPU and how the member functions should be used.

[ye-luo]

Test this please