The private getBomEntryUnitPrice() in ProjectBomEntriesDataTable was
identical to the one in ProjectBuildHelper. Replaced it with a new
public getEntryUnitPrice() on ProjectBuildHelper (returns BigDecimal,
never null) and delegate to it from the DataTable.
This eliminates the duplicate code and brings the DataTable lines under
the existing ProjectBuildHelper test coverage. Added three tests for
getEntryUnitPrice() covering the no-pricing, non-part, and part cases.
Covers calculateTotalBuildPrice(), calculateUnitBuildPrice(),
roundedTotalBuildPrice(), and the private getBomEntryUnitPrice()
helper. Scenarios tested: empty project, no pricing data, non-part BOM
entries with manual prices, part entries with pricedetails, mixed
entries, rounding-up of sub-cent prices, and minimum order amount
floor for price tier lookup.
