Enable arraycontext + lazy evaluation + loop fusion

[a-alveyblanc]

Initial work toward enabling lazy evaluation and compilation. Builds on #139.

A fair amount of work is left to be done. For example:

• Tests need to run with PytatoPyOpenCLArrayContext
• Compilation needs to work
  • Change/remove the use of "views" of arrays
  • Change in-place updating of arrays (probably in a much more principled way than what's been done so far)
• Implement transformations, e.g. loop fusion (maybe this is best done in another PR after lazy + compilation are working)
• Outstanding TODOs from Transition to arraycontext #139

The list above is not exhaustive. The work so far has been toward enabling PytatoPyOpenCLArrayContext and PyOpenCLArrayContext to be valid options. However, compilation does not work.

[alexfikl]

Having worked on #139.. Yeah, there's still a lot of work to get sumpy working nicely with arraycontext 😢

[inducer]

Thanks for getting the work on this started. I agree that it's a big job, we'll get it done with time. I suspect we should only keep one of #139 and this. Any thoughts?

[alexfikl]

Thanks for getting the work on this started. I agree that it's a big job, we'll get it done with time. I suspect we should only keep one of #139 and this. Any thoughts?

Maybe we can make a branch with #139 in the main repository (instead of my fork) and we can work on top of that? Otherwise, I agree with getting the porting to arraycontext in first before trying to use pytato.

[a-alveyblanc]

Maybe we can make a branch with #139 in the main repository (instead of my fork) and we can work on top of that?

I think something like this makes the most sense.