use yaml struct to return n_read var

[ben-schwen]

Follows #7552

Currently yaml in other.Rraw tests are failing

Test 16.02 produced 1 errors but expected 0
Expected: 
Observed: object 'n_read' not found

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.02%. Comparing base (ee23077) to head (8c01c72).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7579   +/-   ##
=======================================
  Coverage   99.02%   99.02%           
=======================================
  Files          87       87           
  Lines       16758    16758           
=======================================
  Hits        16595    16595           
  Misses        163      163           

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[github-actions]

• HEAD=yaml_struct stopped early for DT[,.SD] improved in #4501
• HEAD=yaml_struct slower P<0.001 for memrecycle regression fixed in #5463
  

Generated via commit 8c01c72

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	5 minutes and 10 seconds
Installing different package versions	11 minutes and 8 seconds
Running and plotting the test cases	4 minutes and 3 seconds