Make RhpcBLASctl Suggests?

{RhpcBLASctl} is AGPL-licensed, which makes it invalid for import at many orgs, Google included:

https://opensource.google/documentation/reference/using/agpl-policy

The RhpcBLASctl author confirmed this choice is intentional, but it makes using downstream packages like {rsparse} difficult as well.

To use it, I've patched out the requirement, which AFAICT is about supporting parallelism for performance.

Because it will just make the code slower, I think making {RhpcBLASctl} optional makes sense to more readily support users who can't install it.

Would you accept a PR?