[P2] util.js: relocate token / contract / price helpers to token-util

**Parent Epic:** [#44552 — `util.js` decomposition](https://github.com/MetaMask/metamask-extension/issues/44552)
**Source:** `ui/helpers/utils/util.js`
**Size:** M

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## Problem

`getContractAtAddress`, `checkTokenIdExists`, `getCalculatedTokenAmount1dAgo`, `fetchTokenExchangeRates` (fan-out ~8) are token-subject helpers.

## Solution

Move to `ui/helpers/utils/token-util.js` (the token subject module; the move also advances its own TS migration). `getContractAtAddress` may instead go to `shared/lib/contract-utils.ts` next to `readAddressAsContract` if a shared home is preferred. Codemod the ~8 `fetchTokenExchangeRates` import sites.

## Acceptance Criteria

- [ ] Helpers relocated; originals deleted; import sites rewired (codemod). Tests green.

Start in ui/helpers/utils/util.js and compare the token-related helpers with ui/helpers/utils/token-util.js. Trace the roughly eight fetchTokenExchangeRates import sites, and consider shared/lib/contract-utils.ts for getContractAtAddress alongside readAddressAsContract. Done means the helpers are relocated, originals deleted, imports rewired, and tests are green.

Written by the indexing model from the issue text.