Fix Imputer so that it does not erase ww info during transform

[freddyaboulton]

Pull Request Description

Fixes #2751

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[codecov]

Codecov Report

Merging #2752 (b84057a) into main (411a0c1) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main   #2752     +/-   ##
=======================================
+ Coverage   99.9%   99.9%   +0.1%     
=======================================
  Files        301     301             
  Lines      27827   27840     +13     
=======================================
+ Hits       27778   27791     +13     
  Misses        49      49             

Impacted Files	Coverage Δ
...elines/components/transformers/imputers/imputer.py	100.0% <100.0%> (ø)
evalml/tests/component_tests/test_imputer.py	100.0% <100.0%> (ø)

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[chukarsten]

Nice! Thanks Freddy!

[angela97lin]

Looks good, thanks for filing and fixing this!

This, along with the few other bugs that have popped up re ww typing, makes me wonder what we could do to make this easier--right now, our components could have potentially different behavior if they weren't fully updated to use ww like the imputer was. No real action, just food for thought 😅

[freddyaboulton]

@angela97lin Agreed that it's not comforting to uncover these bugs one-by-one. I will say that the reason that the Imputer did not go through the ww accessor prior to handing the data to the simple imputer is that it didn't need to! The ww type inference used to be almost entirely dependent on the pandas dtype so the simple imputer inference would match the Imputer logical types. Maybe it was always a bug waiting to happen but this implementation got us pretty far.

What I'm saying is that as ww inference evolves and matures so will our code because new corner cases that couldn't exist before will begin to exist.

I think it could help if we always went through the accessor and never "broke" the schema, i think #2744 can help with that.