Validate split rules sum does not exceed 100% for Percentage type

[MarcusDavidG]

When multiple Percentage split rules are provided, the contract does not validate that their basis points sum to <= 10,000. If the sum exceeds 10,000 the contract will attempt to transfer more than the funded amount causing an arithmetic error. Add validation in create_invoice.

[Hassanmovic98]

I will add validation during invoice creation to enforce that all percentage split rules remain within the allowed 10,000 basis point limit. The contract will reject invalid split configurations before any transfer logic executes, preventing arithmetic failures and protecting invoice settlement integrity. Tests will cover valid splits, boundary cases, and over-allocation scenarios.