Use copy on write collection for tracking stored files

[fractalwrench]

Goal

Tracing of the delivery layer from flaky tests indicates that the payload store is erroneously telling the scheduling service that 0 payloads are persisted on disk. I'm suspicious that this might be due to the implementation of storedFiles in getPayloadByPriority as it uses a ConcurrentSkipListSet, whose operations are async. I'd hypothesise that in our tests and also in prod this can result in a race condition where payloads aren't delivered by the scheduling service on the first attempt (although subsequent attempts do result in delivery).

Altering the implementation to use CopyOnWriteArraySet should fix this if the theory is correct.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

OpenSSF Scorecard

Package	Version	Score	Details

Scanned Files

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.18%. Comparing base (341006b) to head (29709ee).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1708   +/-   ##
=======================================
  Coverage   84.17%   84.18%           
=======================================
  Files         457      457           
  Lines       10676    10674    -2     
  Branches     1606     1606           
=======================================
- Hits         8987     8986    -1     
  Misses        957      957           
+ Partials      732      731    -1     

Files with missing lines	Coverage Δ
...rnal/delivery/storage/PayloadStorageServiceImpl.kt	80.00% <100.00%> (-0.52%)	⬇️

... and 1 file with indirect coverage changes

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[bidetofevil]

LGTM