REFACTOR: Refactor full_axis argument

[RehanSD]

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full_axis at the virtual partition level is used as a flag to tell the partition whether to block partition after or to materialize the result as a single partition - we should probably change it from full_axis to a more descriptive name that better reflects its usage.

[mvashishtha]

I think we can also stop making it a property of the axis object, and instead control the full_axis behavior with arguments to apply. apply seems to be the only thing that uses the full_axis argument.

edit: Or perhaps even better, always make apply return a single partition, and split the result with another method.