[Typescript Conversion: Level 19]: Convert ui/selectors/transactions.js to typescript

## **Description**

Convert `ui/selectors/transactions.js` from JavaScript to TypeScript as part of the TS migration initiative.

## **Scenario (for user stories only)**

_(Not applicable)_

## **Design (for user stories only)**

_(Not applicable)_

## **Technical Details (for technical tasks only)**

- Convert this file to TypeScript.
- Migration Level: **19**
- Dependencies:
- shared/constants/transaction.ts
- shared/modules/conversion.utils.ts
- ui/helpers/constants/transactions.js
- ui/helpers/utils/tx-helper.ts
- Dependents:
- ui/components/app/transaction-list/transaction-list.component.js
- ui/selectors/confirm-transaction.js
- ui/selectors/index.js
- ui/selectors/nonce-sorted-transactions-selector.test.js
- ui/selectors/selectors.js

## **[Threat Modeling Framework](https://github.com/adamshostack/4QuestionFrame) (for technical tasks only)**

- What are we working on? Convert file to TypeScript.
- What can go wrong? Type errors, integration mismatches, missing types.
- What are we going to do about it? Write types carefully and test thoroughly.
- Did we do a good job? _(To be evaluated)_

## **Acceptance Criteria**

- File is fully converted to TypeScript.
- Tests pass.
- File adheres to linting rules.
- Functionality remains unchanged.

## **Stakeholder Review (for MetaMask employees only)**

- [X] Engineering
- [ ] Design
- [ ] Product
- [ ] QA
- [ ] Security
- [ ] Legal
- [ ] Marketing
- [ ] Management
- [ ] Other

## **References**

- Parent issue: #31460