Adds a skeleton for non conforming kernel implementation [DO NOT MERGE]

[Rohit-Kakodkar]

Description

@int-ptr-ptr I added a skeleton for the non-conforming kernel, which we can fill out after we have the containers. Can you see if this looks right?

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[int-ptr-ptr]

This looks right, but I do wonder about the future, where coupled interfaces have shared computations (for example, jump operators), so it would be faster to accelerate both self and other at the same time.

Since interfaces are $O(N)$ with the length scale resolution, this won't be an issue for Ivy's problem (we can swallow the unoptimized code for now), but it would be something to keep in mind.