FINERACT-2712: Fix duplicate defined name 500 in loan and savings opening templates

[oluexpert99]

  - GET /v1/loans/downloadtemplate and GET /v1/savingsaccounts/downloadtemplate returned
    HTTP 500 (IllegalArgumentException: The workbook already contains this name) on any
    tenant holding two products, or two loan charges, that resolve to the same Excel
    defined name. Both opening templates are unusable for the whole tenant and there is no
    API-side workaround.
  - LoanWorkbookPopulator.setNames and SavingsWorkbookPopulator.setNames create a block of
    per-product (and, for loans, per-charge) defined names keyed by the product or charge
    name, with no de-duplication. The second entry resolving to the same name calls
    Name.setNameName with a name the workbook already holds and POI rejects it. Excel
    defined names are case-insensitive, so names differing only in case or in surrounding
    whitespace collide too -- e.g. products "Target Savings" and "TARGET SAVINGS " both
    produce Interest_Compouding_TARGET_SAVINGS.
  - Guard each loop with a Set of names already emitted and skip a repeat, so every name
    produces its defined-name block exactly once. The key is the sanitised, upper-cased
    name, which is the exact string the workbook will hold, so two source values that
    differ only in stripped punctuation or case are treated as the collision they are.
  - Extract the sanitising step of AbstractWorkbookPopulator.setSanitized into a protected
    sanitizeName helper so the de-duplication key is computed by the same code that builds
    the name, rather than duplicating the regex. setSanitized keeps its behaviour exactly.
  - In both loops the name is now resolved before any createName call, so a skipped
    duplicate leaves no orphan Name object in the workbook.
  - Semantics of the skip: the FIRST entry with a given name keeps the defined name, so the
    dropdown for that name resolves to the first product's or charge's lookup row. The
    second entry's per-product defaults are not reachable through the dropdown -- which is
    inherent to keying defined names by a non-unique field, and is still strictly better
    than failing the download for every user of the tenant. The lookup sheet itself is
    unchanged and still lists every product, so the row indices behind the ranges stay
    correct.
  - Add unit tests for the loan charge loop, the loan product loop and the savings product
    loop. Each fails on the unfixed code with the exact production exception
    (CHARGE_NAME_LATE_FEE, FUND_MICRO_LOAN, Interest_Compouding_TARGET_SAVINGS). Note the
    loan product loop substitutes spaces before sanitising, so a trailing space yields a
    genuinely different name there and only a case-only clash collides; the charge and
    savings loops trim first, so both variants collide.

Description

Describe the changes made and why they were made. (Ignore if these details are present on the associated Apache Fineract JIRA ticket.)

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