Boundary lazy comm v2 (#183)

* Boundary lazy comm v2

* fixes

* use pytato branch

* use staple_distributed_send

* add lazy option to wave-op-mpi

* ci fix

* initial actx support

* _RankBoundaryCommunicationLazy: do not convert to/from numpy, flatten

* Prototype MPIPytatoPyOpenCLArrayContext

* Drop evt.wait in distributed actx

* cross_rank_trace_pairs: set 'unique' tag per obj array component

* Drop commented-out graph vis from mpi+lazy actx

* add clone()

* only use Lazy boundary comm when running with lazy actx

* fix git branch

* remove duplicate requirement

* accept distributed+parallel actx

* wave-op-mpi: add simple timing

* fix MPISingleGridWorkBalancingPytatoArrayContex

* fix spelling

* initial lazy batched comm

* select comm class based on actx

* flake8

* use meshmode lazy actx

* test: use random tag

* undo random tag change

* use random tag again

* another tag fix

* debug tracepair

* add dbg

* more dbg

* Use structured tags for lazily-communicated array containers

* MPISingleGridWorkBalancingPytatoArrayContext: Convert symbolic to numeric comm tags

* more type annotation

* support running eager comm as well

* force SingleGridWorkBalancingPytatoArrayContext

* wave-op-mpi: Fix name of MPI+Pytato array context

* wave-op-mpi: Add missing mpi_communicator arg to DiscretizationCollection

* Distributed actx: deduplicate data wrappers before partitioning

* undo pytato branch

* add loopy req

* test with MPI

* use serial actx if parallel not available

* rework dependency chain

* fix lint

* make wave-op-mpi run without older lazy actx

* adapt to recent arraycontext changes

* use DistributedLazyArrayContext to simplify lazy detection

* document tag arg

* Simplify distributed-lazy array context usage (#218)

* add get_reasonable_array_context_class

* add get_reasonable_array_context_class

* document tag in interior_trace_pairs

* update MPI test infrastructure

* restructure tests

* Weak wave operator: add comm tag

* Generalize MPI test orchestration for lazy

* MPI test: use actx.compile

* test fixes

* fix sin()

* Drop leap from test_mpi_communication

* Add norm assert to test_mpi_communication

* restore final_t

* Introduce an eager-MPI array context with a sym->num tag map

Co-authored-by: Andreas Kloeckner <inform@tiker.net>