Relax empty pencil check during grid descriptor creation to allow more flexibility

[romerojosh]

Alternative version of #102. Fixes #101.

As it stands right now, cuDecomp will not allow users to create grid descriptors that potentially result in situations where processes have empty pencils with zero elements in any pencil orientation (i.e. x-pencils, y-pencils, z-pencils), which is very conservative. Users might desire using cuDecomp on only a subset of the pencil orientations and might not care if the other orientations have empty processes. For example, in #101, that user is interested in using halo-exchange routines on z-pencils with N x N x 1 dimensions. The current empty pencil checks will not allow this usage at all due to the x- and y- pencil orientations attempting to distribute the 1 dimension.

This PR addresses this limitation by:

1. Loosening the empty pencil checks during halo autotuning to only the pencil orientation being tested.
2. Removing the general restriction on creating grid descriptors resulting in empty pencils.

Unlike #102, this PR explicitly disallows running cuDecomp operations on configurations that will encounter empty pencils and throws an error. Effectively, this replaces the more general and conservative empty pencil check in cudecompGridDescCreate to more targeted check that only triggers if a user attempts an unsupported operation. This ultimately makes the library more flexible by allowing more use cases, but also does not add the complexity of handling communicators with empty pencils.

[romerojosh]

/build

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