Better Ensure reduce returns a NestedFrame

[dougbrn]

Change Description

Resolves #54

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Solution Description

The issue seems to be that when meta is passed using dask's shorthand notation of dicts and tuples, the result is interpreted as a dask result. All this PR does is get in front of Dask whenever these shorthands are used, and casts them to npd.NestedFrames (even in the case of a series result as is consistent with Nested-Pandas)

I originally intended to wrap map_partitions (so ignore branch name), but believe this is unnecessary as meta handling works as expected for npd.NestedFrame meta

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[github-actions]

Before [f3b201e] <v0.2.1>	After [c9d94a8]	Ratio	Benchmark (Parameter)
151M	153M	1.01	benchmarks.NestedFrameAddNested.peakmem_run
228±0.5ms	230±2ms	1.01	benchmarks.NestedFrameAddNested.time_run
151M	154M	1.01	benchmarks.NestedFrameQuery.peakmem_run
149M	151M	1.01	benchmarks.NestedFrameReduce.peakmem_run
475±2ms	474±2ms	1	benchmarks.NestedFrameQuery.time_run
234±1ms	232±2ms	0.99	benchmarks.NestedFrameReduce.time_run

Click here to view all benchmarks.

[smcguire-cmu]

Looks good, thanks! Just one little thing to add to the tests