refactor(storage)!: Make ReadObjectResponse a trait

[dbolduc]

Fixes #2901, and helps with #2041

Conflicts with #2907. @suzmue - I am happy to do this in either order. I had to introduce extra guarantees on the C: ChecksumEngine to make this work.... but none of that would be necessary if there was no C to begin with.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.17%. Comparing base (0b0c908) to head (cec272c).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2931   +/-   ##
=======================================
  Coverage   96.17%   96.17%           
=======================================
  Files         105      105           
  Lines        4393     4394    +1     
=======================================
+ Hits         4225     4226    +1     
  Misses        168      168           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.