Feat: implemented get_project_transactions function

[caxtonacollins]

closes #46

• Added a double map storage pattern to track transaction IDs per project.
• Implemented get_project_transactions with pagination (page, page_size) and robust input validation.
• Updated create_transaction to maintain the project-to-transaction mapping.
• Added comprehensive unit tests covering:
• Pagination and edge cases (no transactions, single transaction, invalid parameters)
• Data integrity and correct ordering
• Multiple project isolation
• Added NatSpec documentation to both the interface and contract implementation.

[caxtonacollins]

closes #46 please review

[anonfedora]

Hi @caxtonacollins, your PR isn't passing the CI, and I'm yet to.hear from you, I need a PR within 6 hours or I'd have to reassign

[anonfedora]

Fix conflicts, please

[caxtonacollins]

closes #46
@anonfedora Fixed