M. Eric Irrgang authored Feb 10, 2022 and Sebastian Wingbermühle committed Feb 10, 2022

Task isolation, work deduplication, and MPI safety.

* Make gmxapi.operation compatible with MPI-based ensemble management.
* Deduplicate work across MPI ranks.
* Synchronize results across MPI ranks.
* Isolate gmxapi.commandline_operation working directories.
* Ensemble width for subgraph variables and their updates is now clarified when the subgraph instance is built.
* `while_loop` explicitly behaves as an AllGather of the results it wraps, and correctly represents ensemble outputs as having an array dimension.
* Naming of nodes in the workflow graph (operation instance identifiers) is clarified, normalized, and made consistent across the ensemble for operations in `gmxapi.simulation` module.
* A distinction is clarified between work that **is** and **is not** duplicated on each MPI rank.
* A new `allow_duplicate` annotation determines whether tasks should be launched on all ranks, or whether they should run on a single rank and share their results.
* Futures provided by the user to the subgraph may block the propagation of `reset()` to data providers.
* Finalize gmxapi 0.3.0 release.

Closes #3138