Fix thread safety issue in consistency pipeline

[jbrooks-stripe]

Summary

This changes things such that a new instance of the AvroCodec is used instead of re-using the same one across requests.

Why / Goal

To log feature values for the consistency pipeline, we use AvroCodec to encode and hash keys, but the Avro encoding here is not thread safe.

Test Plan

• [x] Added Unit Tests
• [x] Covered by existing CI
• [ ] Integration tested

Checklist

• [ ] Documentation update

Reviewers

[hzding621]

Ah missed this, I will fix it in https://github.com/airbnb/chronon/pull/857!