fix(billing): replace $sortArray with portable $unwind+$sort+$group (MongoDB 5.0.x compat)

[PierreBrisorgueil]

Summary

• Replaces $sortArray (MongoDB ≥5.2) in listLedgerPage with a portable $unwind → $sort → $group pipeline compatible with MongoDB ≥4.4
• Adds a $filter guard in the final $project to prevent a null sentinel entry in ledgerPage when the ledger array is empty (edge case exposed by preserveNullAndEmptyArrays)
• Adds 7 unit tests for listLedgerPage (input guards, sort order, empty result, portability regression guard) and 1 integration test for the empty-ledger edge case

Closes #3774

Test plan

• npm run test:unit — 1740/1740 pass (includes 7 new unit tests for listLedgerPage)
• Integration tests for listLedger.perf — 5/5 pass on mongodb-memory-server (proves MongoDB 5.0.x portability)
• npm run lint — clean
• CI on GitHub runners

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📥 Commits

Reviewing files that changed from the base of the PR and between 690e756 and cff1391.

📒 Files selected for processing (3)

• modules/billing/repositories/billing.extraBalance.repository.js
• modules/billing/tests/billing.extraBalance.listLedger.perf.integration.tests.js
• modules/billing/tests/billing.extraBalance.unit.tests.js

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• Create PR with unit tests
• Commit unit tests in branch fix/billing-sortarray-mongo52

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.23%. Comparing base (428fb18) to head (cff1391).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3796   +/-   ##
=======================================
  Coverage   90.23%   90.23%           
=======================================
  Files         152      152           
  Lines        5026     5028    +2     
  Branches     1599     1600    +1     
=======================================
+ Hits         4535     4537    +2     
  Misses        386      386           
  Partials      105      105           

Flag	Coverage Δ
integration	59.06% <ø> (-0.03%)	⬇️
unit	69.76% <ø> (+0.13%)	⬆️

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[Copilot]

Pull request overview

This PR updates BillingExtraBalanceRepository.listLedgerPage to avoid the MongoDB 5.2+ $sortArray operator by switching to a portable $unwind → $sort → $group pipeline, and adds regression tests around ordering and the empty-ledger edge case.

Changes:

• Replaces $sortArray usage in listLedgerPage with a portable aggregation pipeline ($unwind + $sort + $group) and filters out the null sentinel produced for empty arrays.
• Adds unit tests covering listLedgerPage input guards, null return behavior, ordering expectations, and a $sortArray regression guard.
• Adds an integration test to ensure an empty ledger returns ledgerPage: [] (not [null]).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
modules/billing/repositories/billing.extraBalance.repository.js	Reworks the aggregation pipeline to avoid $sortArray and adds an empty-ledger guard via $filter.
modules/billing/tests/billing.extraBalance.unit.tests.js	Adds unit tests for listLedgerPage behavior and a portability regression guard against $sortArray.
modules/billing/tests/billing.extraBalance.listLedger.perf.integration.tests.js	Adds an integration regression test for the empty-ledger [null] sentinel case.