Remove `getMemoizedInterface(s)` deep-equal wrappers in `interfaceController` once input stability is verified

> **Performance audit finding** · Severity: **Low** · Effort: Easy · Fix risk: Simple · Test safety net: Partial
> Owner: CODEOWNERS best-effort (snaps)
> File: `app/selectors/snaps/interfaceController.ts:27,43`

### What is this about?

`getMemoizedInterfaces` and `getMemoizedInterface` are `createDeepEqualSelector` wrappers whose `getMemoized*` naming marks them as band-aids added downstream of unstable inputs. Deep-equal selectors run a deep comparison on every evaluation; if the underlying input slice is reference-stable when unchanged, plain `createSelector` suffices and the deep compares are pure overhead. If the input genuinely is replaced wholesale, the wrapper is justified — verify which contract holds before changing anything.

### Technical Details

Log `prev === next` for the input slice across two unrelated dispatches (the reference-stability contract test). Stable: downgrade both to `createSelector` and delete the `getMemoized` prefix. Unstable: keep, and document why at the definition so the next audit doesn't re-flag it. `getMemoizedInternalAccountByAddress` (the third wrapper found by the sweep) is filed separately with a different fix: #31491.

### Acceptance Criteria

- Contract verified and recorded; wrappers downgraded or annotated accordingly.

### References

- File: `app/selectors/snaps/interfaceController.ts:27,43`
- Source: `mms-performance` sweep recipes added in MetaMask/skills#49 (`mm-selector-cascade` — band-aid sweep)
- Status: **UNVALIDATED** (static evidence)

Start in app/selectors/snaps/interfaceController.ts at lines 27 and 43, and inspect the inputs to getMemoizedInterfaces and getMemoizedInterface. Verify input reference stability across two unrelated dispatches, recording the contract; done means either replacing both wrappers with createSelector and removing the prefixes, or documenting why the wrappers remain.

Written by the indexing model from the issue text.