refactor: Remove DataBuf from ReadResponse

[vipnydav]

Description

This PR removes the DataBuf field from the ReadResponse struct. This is because the DataBuf field is redundant, as the same slice is passed to ReadAt methods and written to, and the caller already has access to the modified slice. This change simplifies the code by removing the need for repeated assignments.

Link to the issue in case of a bug fix.

b/458976462

Testing details

1. Manual - Done
2. Unit tests - NA
3. Integration tests - Automated

Any backward incompatible change? If so, please explain.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.08%. Comparing base (3016128) to head (4298eaf).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3993      +/-   ##
==========================================
- Coverage   83.11%   83.08%   -0.03%     
==========================================
  Files         148      148              
  Lines       18187    18183       -4     
==========================================
- Hits        15116    15108       -8     
- Misses       2520     2523       +3     
- Partials      551      552       +1     

Flag	Coverage Δ
unittests	83.08% <100.00%> (-0.03%)	⬇️

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