chore: Fix typing

[felixwang9817]

What this PR does / why we need it: This PR removes Array and String and other Feast types as top-level objects, so that users must do from feast.types import Array, String instead of feast import Array, String.

Which issue(s) this PR fixes:

Fixes #

[achals]

/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: achals, felixwang9817

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[codecov-commenter]

Codecov Report

Merging #2534 (f89ecc6) into master (6f22f22) will decrease coverage by 0.18%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2534      +/-   ##
==========================================
- Coverage   81.78%   81.60%   -0.19%     
==========================================
  Files         141      141              
  Lines       11939    12000      +61     
==========================================
+ Hits         9764     9792      +28     
- Misses       2175     2208      +33     

Flag	Coverage Δ
integrationtests	73.56% <77.77%> (-0.61%)	⬇️
unittests	57.63% <100.00%> (+0.04%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
sdk/python/feast/__init__.py	91.30% <ø> (-0.37%)	⬇️
sdk/python/tests/doctest/test_all.py	89.83% <100.00%> (+0.17%)	⬆️
...tegration/feature_repos/universal/feature_views.py	83.33% <100.00%> (ø)
.../integration/online_store/test_universal_online.py	92.59% <100.00%> (-0.84%)	⬇️
...istration/test_universal_odfv_feature_inference.py	100.00% <100.00%> (ø)
...ests/integration/scaffolding/test_partial_apply.py	100.00% <100.00%> (ø)
sdk/python/feast/wait.py	58.82% <0.00%> (-35.30%)	⬇️
sdk/python/tests/utils/online_read_write_test.py	93.54% <0.00%> (-6.46%)	⬇️
sdk/python/feast/request_feature_view.py	62.50% <0.00%> (-5.07%)	⬇️
.../integration/online_store/test_online_retrieval.py	96.84% <0.00%> (-3.16%)	⬇️
... and 9 more

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[achals]

/lgtm

[feast-ci-bot]

New changes are detected. LGTM label has been removed.