[Sparse] Add clear_triplets()

[lsh]

This PR adds the clear_triplet() method to the CooMatrix struct.
The goal of the method is to be able to remove triplets before construction.

Some outstanding questions:

• Spelling of the method? @Andlon suggested clear_triplet in the Discord. Another option might be pop or pop_triplet to correspond to push.
• Should out of bounds values cause a panic? It is probably fine to just return a None value.
• What should the return type be? Currently it is Option<T>.

[Andlon]

Thanks for working on this @lsh!

Actually, I suggested clear_triplets (note plural), for removing all triplets. This is very useful as it would allow us to re-use already allocated COO storage and therefore amortize allocations. I'm not so sure if removing a single triplet based on coordinates is very useful as it is terribly inefficient - do we have a compelling motivating use case for this?

[lsh]

@Andlon whoops, sorry about my misunderstanding 😅. Updated the code to implement clear_triplets.

[Andlon]

@lsh: great, thanks. CI is failing because you have the wrong return type for clear_triplets, maybe try running tests locally?

[Andlon]

@lsh: just one unnecessary trait bound that needs to be removed, otherwise looks good! Tests are still running but assuming they succeed after removing the trait bound we should be good to go.

[Andlon]

@sebcrozet: not sure why the CUDA build is failing. Do you? Looks like some strange issues with the recent changes that made Point::new a const fn?

[sebcrozet]

@Andlon You’re right, looks like #1112 broke the CUDA build (and for some reasons the CI didn’t run of that PR). I think this is due to the fact that the CUDA build uses an older version of the compiler which only allowed Sized trait bounds for const fn. We should add a non-const version when targeting cuda.

[Andlon]

Looks good to me, ready for merge. @sebcrozet: do we wait with merging until the CUDA CI problems are fixed, or what's your preference?

[sebcrozet]

Thank you both! No need to delay this on something unrelated.