DM-53882: Modify Instrument.importAll to return the instruments it imported

[timj]

Checklist

• ran Jenkins
• ran and inspected package-docs build
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.85%. Comparing base (1b2746f) to head (b5fbace).
⚠️ Report is 8 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #542      +/-   ##
==========================================
- Coverage   88.90%   88.85%   -0.06%     
==========================================
  Files         154      154              
  Lines       21304    21309       +5     
  Branches     2515     2515              
==========================================
- Hits        18941    18934       -7     
- Misses       1769     1776       +7     
- Partials      594      599       +5     

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[srp3rd]

No comments - looks fine