[Refactor] Rename / Refactor `shared/lib/transactions-controller-utils.js` file

**What is this about?**

As discussed in https://github.com/MetaMask/metamask-extension/pull/25799#discussion_r1680660006, `TransactionController` no longer lives directly in the repo. We should rename or refactor `shared/lib/transactions-controller-utils.js` accordingly. Consider filename(s): `shared/lib/[math|large-number|decimals].ts`

**Stakeholder review needed before the work gets merged**

- [ ] Engineering (needed in most cases)
- [ ] Design
- [ ] Product
- [ ] QA (automation tests are required to pass before merging PRs but not all changes are covered by automation tests - please review if QA is needed beyond automation tests)
- [ ] Security
- [ ] Legal
- [ ] Marketing
- [ ] Management (please specify)
- [ ] Other (please specify)

Read the linked pull request discussion first, then inspect shared/lib/transactions-controller-utils.js and its references. Determine whether the utilities belong under math, large-number, or decimals, and update the filename and references consistently; done means the obsolete TransactionController-specific naming is removed and the relevant checks pass.

Written by the indexing model from the issue text.