fix for empty query results

[dougbrn]

Change Description

Resolves #129.

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Solution Description

This PR addresses an issue flagged in #129. Where queries that return empty results in at least one partition on the nested-dask side can result in an error. This issue is not reproducible within Nested-Pandas, as it's a result of Dask's sensitivity to metadata and dtyping. The issue being that the empty series we produce from an empty query did not specify an index with identical name and dtype (the dtype being the important piece). This PR makes the small tweak of propagating the correctly dtype'd index.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.44%. Comparing base (71ae3ba) to head (743de7b).
Report is 72 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #128   +/-   ##
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  Coverage   99.44%   99.44%           
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  Files          14       14           
  Lines         897      897           
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  Hits          892      892           
  Misses          5        5           

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[github-actions]

Before [5a6ab4a]	After [9b21ddb]	Ratio	Benchmark (Parameter)
32.6±1ms	33.7±2ms	1.03	benchmarks.AssignSingleDfToNestedSeries.time_run
260M	262M	1.01	benchmarks.AssignSingleDfToNestedSeries.peakmem_run
87.1M	87.1M	1	benchmarks.NestedFrameAddNested.peakmem_run
94.1M	94M	1	benchmarks.NestedFrameQuery.peakmem_run
90.6M	90.7M	1	benchmarks.NestedFrameReduce.peakmem_run
60.3±3ms	59.5±3ms	0.99	benchmarks.ReassignHalfOfNestedSeries.time_run
284M	278M	0.98	benchmarks.ReassignHalfOfNestedSeries.peakmem_run
1.12±0.03ms	1.08±0.02ms	0.97	benchmarks.NestedFrameReduce.time_run
6.88±0.3ms	6.33±0.1ms	0.92	benchmarks.NestedFrameQuery.time_run
10.1±0.2ms	9.04±0.1ms	0.9	benchmarks.NestedFrameAddNested.time_run

Click here to view all benchmarks.

[wilsonbb]

Looks good!

Approving, but can we add a small accessor unit test for query flat's empty case? Then we can verify there that the index is getting propagated