[Typescript Conversion: Level 18]: Convert shared/modules/swaps.utils.js to typescript

## **Description**

Convert `shared/modules/swaps.utils.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: **18**
- Dependencies:
- shared/constants/swaps.ts
- Dependents:
- ui/hooks/useSwappedTokenValue.js
- ui/pages/swaps/awaiting-swap/awaiting-swap.js
- ui/pages/swaps/swaps.util.ts

## **[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

Start with shared/modules/swaps.utils.js and its dependency shared/constants/swaps.ts, then inspect the listed UI dependents for compatibility expectations. Run the relevant swaps tests and lint checks. Done means the utility is fully TypeScript, functionality is unchanged, and all tests and linting pass.

Written by the indexing model from the issue text.