Python FeatureServer optimization

[judahrand]

What this PR does / why we need it:
Previously, the Python FeatureServer was doing pointless conversion of Protobuf entity values to Python native types only to convert them back again.

This PR is stacked on top of #2186 so only the last commit is relevant to the issue.

Which issue(s) this PR fixes:

Fixes #2201

Does this PR introduce a user-facing change?:

None

[codecov-commenter]

Codecov Report

Merging #2202 (65dea14) into master (1b98ec9) will increase coverage by 25.12%.
The diff coverage is 78.08%.

@@             Coverage Diff             @@
##           master    #2202       +/-   ##
===========================================
+ Coverage   59.83%   84.96%   +25.12%     
===========================================
  Files         105      105               
  Lines        8453     8493       +40     
===========================================
+ Hits         5058     7216     +2158     
+ Misses       3395     1277     -2118     

Flag	Coverage Δ
integrationtests	73.12% <78.08%> (?)
unittests	59.73% <73.97%> (-0.11%)	⬇️

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

Impacted Files	Coverage Δ
sdk/python/feast/feature_server.py	31.57% <0.00%> (+0.80%)	⬆️
sdk/python/feast/feature_store.py	90.13% <80.28%> (+17.31%)	⬆️
sdk/python/feast/data_source.py	61.29% <0.00%> (+0.40%)	⬆️
sdk/python/feast/infra/online_stores/sqlite.py	94.48% <0.00%> (+0.78%)	⬆️
sdk/python/feast/online_response.py	77.77% <0.00%> (+3.70%)	⬆️
sdk/python/feast/feature.py	90.24% <0.00%> (+4.87%)	⬆️
sdk/python/feast/errors.py	71.01% <0.00%> (+5.07%)	⬆️
sdk/python/feast/infra/provider.py	89.65% <0.00%> (+5.17%)	⬆️
sdk/python/feast/infra/offline_stores/file.py	97.60% <0.00%> (+8.79%)	⬆️
... and 53 more

---

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[achals]

@judahrand is this ready for review? Now that #2186 has been merged.

[judahrand]

@judahrand is this ready for review? Now that #2186 has been merged.

I'm struggling to work out why the FeatureServer tests are failing and don't have a good way to debug since the FeatureServer is only supported by the AWS test 🤔

[adchia]

/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: adchia, judahrand

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