Add Basic Dask Support

[ghost]

Following up on the discussion in #647 and related to #119, this PR adds basic dask support as optional extra functionality. When a pandera schema validates a dask dataframe, it maps the validation operation to each of the partition pandas dataframes.

With dask installed:

import pandera as pa
from pandera.typing import DaskDataFrame


class MySchema(pa.SchemaModel):
    col: Series[int]


@pa.check_types
def f(df: DaskDataFrame[MySchema]):
    ...

[codecov]

Codecov Report

Merging #665 (de89c9d) into release/0.8.0 (0236dae) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@                Coverage Diff                @@
##           release/0.8.0     #665      +/-   ##
=================================================
+ Coverage          98.35%   98.40%   +0.04%     
=================================================
  Files                 31       32       +1     
  Lines               3580     3625      +45     
=================================================
+ Hits                3521     3567      +46     
+ Misses                59       58       -1     

Impacted Files	Coverage Δ
pandera/__init__.py	100.00% <100.00%> (ø)
pandera/check_utils.py	100.00% <100.00%> (ø)
pandera/dask_accessor.py	100.00% <100.00%> (ø)
pandera/schemas.py	99.52% <100.00%> (+0.01%)	⬆️
pandera/typing.py	93.39% <100.00%> (+0.76%)	⬆️
pandera/pandas_accessor.py	100.00% <0.00%> (+3.44%)	⬆️

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[cosmicBboy]

hey @bphillips-exos so the lack of coverage is because we need to add dask to ci-test.yml like so:

https://github.com/pandera-dev/pandera/blob/release/0.8.0/.github/workflows/ci-tests.yml#L148-L153

[ghost]

Thanks @cosmicBboy, the diff is fully covered now. It's unclear to me why the project wide coverage has decreased though, I'll take another look at that. Is there anything else you'd like me to address?

[cosmicBboy]

hi @bphillips-exos no worries, as long as the patch has full coverage it's fine.

[cosmicBboy]

great work @bphillips-exos ! 🚀