Bugfix/763: DataFrameModel validate returns the correct type

[chadwhawkins]

Updates the return type casting of various model methods to return the correct type (DataFrame instead of DataFrameBase). The issue called for typing overload but that didn't seem to be necessary in looking at the code, because as best as I can tell calling these methods should always return the same thing (and DataFrame inherits from DataFrameBase anyway).

Resolves #763

[cosmicBboy]

Hi @chadwhawkins, so unfortunately this will introduce another issue, which is that these methods can also return modin, pyspark.pandas, and dask dataframes. The current typing is also incorrect, but we actually do need to do type overloading here to cover those other dataframe types.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (812b2a8) 94.28% compared to head (08efe7a) 94.28%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1450      +/-   ##
==========================================
- Coverage   94.28%   94.28%   -0.01%     
==========================================
  Files          91       91              
  Lines        7013     7011       -2     
==========================================
- Hits         6612     6610       -2     
  Misses        401      401              

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[chadwhawkins]

Ah ok, thanks @cosmicBboy. I'll continue iterating on this PR.

[cosmicBboy]

Thanks @chadwhawkins let me know when you need a review on this

[cosmicBboy]

@chadwhawkins you can rebase on main to address the linter errors: #1468

[chadwhawkins]

Thanks @cosmicBboy, planning to revisit this soon