FINERACT-2421: Fix shortName collisions in integration tests by routing all generation through uniqueRandomStringContainer

[oleksii-novikov-onix]

Description

• Fix flaky integration tests that intermittently fail with duplicate.short.name error
• Three places generated loan product shortName bypassing uniqueRandomStringContainer, causing collisions within the same JVM/DB

The error has occurred several times recently in GA:

CallFailedRuntimeException: HTTP failed: ...url=https://localhost:8443/fineract-provider/api/v1/loanproducts...
  errorBody: {"defaultUserMessage":"Loan product with short name `EA12` already exists",
  "userMessageGlobalisationCode":"error.msg.product.loan.duplicate.short.name"}

Failed job example https://github.com/apache/fineract/actions/runs/24211276415/job/70680889530

Root cause:
FeignLoanHelper and FeignTrialBalanceSummaryReportTest used UUID.randomUUID().substring(0,4), and WorkingCapitalLoanDelinquencyActionIntegrationTest used Utils.randomStringGenerator() - all bypassing the in-memory uniqueRandomStringContainer. Later calls to uniqueRandomStringGenerator() could generate the same value, resulting in a DB unique constraint violation.

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