Add missing test coverage for SettlementDomainService

[Copilot]

Each method in SettlementDomainService lacked tests for several failure and alternate-schedule paths. Adds 10 new unit tests across all three methods.

ProcessSettlement

• GetSettlementAggregateFailed — GetLatest<SettlementAggregate> returns a failure result
• GetMerchantFailed — Get<MerchantAggregate> returns a failure result (existing test only covered ThrowsAsync)
• GetTransactionFailed — GetLatest<TransactionAggregate> returns a failure result (same gap as above)
• SaveSettlementAggregateFailed — non-retryable (non-WrongExpectedVersion) save failure on the scheduled path
• WithScheduledSettlement_SettlementIsProcessed — happy path with SettlementSchedule.Weekly; all existing happy-path tests used Immediate via CreatedMerchantAggregate()

AddMerchantFeePendingSettlement

• GetSettlementFailed — GetLatest<SettlementAggregate> returns failure
• SaveFailed — Save returns failure
• ExceptionThrown — unhandled exception caught by the method's try/catch

AddSettledFeeToSettlement

• GetSettlementFailed — GetLatest<SettlementAggregate> returns failure
• WithScheduledSettlement_FeeAdded — exercises MarkFeeAsSettled (scheduled path) via SettlementSchedule.Weekly; all existing tests hit the Immediate path via CreatedMerchantAggregate()

Warning

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I tried to connect to the following addresses, but was blocked by firewall rules:

• f.feedz.io
  • Triggering command: /usr/bin/dotnet dotnet test TransactionProcessor.BusinessLogic.Tests/TransactionProcessor.BusinessLogic.Tests.csproj --filter FullyQualifiedName~SettlementDomainService --no-build -v n (dns block)
  • Triggering command: /usr/bin/dotnet dotnet test TransactionProcessor.BusinessLogic.Tests/TransactionProcessor.BusinessLogic.Tests.csproj --filter FullyQualifiedName~SettlementDomainService -v n (dns block)
  • Triggering command: /opt/hostedtoolcache/CodeQL/2.24.0/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp /opt/hostedtoolcache/CodeQL/2.24.0/x64/codeql/csharp/tools/linux64/Semmle.Autobuild.CSharp (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
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Original prompt

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This section details on the original issue you should resolve

<issue_title>Update Test Coverage on Settlement Domain service</issue_title>
<issue_description>Each domain service method needs new tests added to cover all cases</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Update Test Coverage on Settlement Domain service #929

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