Memory arena for launch

[artv3]

Summary

This PR introduces the concept of a memory arena of launch. The underlying idea is to allow users to allocate static shared memory (or could be an external memory type?) and manage it through a bump style allocator.

This PR is a work in progress.

[artv3]

@YohannDudouit , I'm thinking the shared memory arena that we talked about could look be implemented something like this? At the moment I'm not sure how we can differentiate between static or dynamically allocated shared memory. What do you think?

[artv3]

@tomstitt , adding you in the loop since I think we talked about this as well.