[P2] util.js: relocate date/time formatters to a new date module

**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

`formatDate` (fan-out ~9), `formatUTCDateFromUnixTimestamp`, `formatDateWithYearContext`, `toHumanReadableTime` — Luxon-based formatters with no existing date-module home. `toHumanReadableTime` takes the i18n `t` fn (UI-coupled).

## Solution

Create `ui/helpers/utils/date.ts` (TypeScript) and move the formatters there (keep `toHumanReadableTime` UI-side via `t`). Codemod the ~9 `formatDate` import sites.

## Acceptance Criteria

- [ ] New `ui/helpers/utils/date.ts`; formatters moved; originals deleted; imports rewired. Tests green.

Start with ui/helpers/utils/util.js and trace the roughly nine formatDate import sites, then review the existing formatter tests before creating ui/helpers/utils/date.ts. Done means the four formatters are moved, originals are deleted, imports are rewired, and the test suite is green.

Written by the indexing model from the issue text.