feat(tron-wallet-snap): route asset reads through Core when migration is on

[ulissesferreira]

Summary

• Pass RemoteFeatureFlagsProvider into AssetsService and resolve the Tron assets migration flag via #shouldReturnAssetsFromCore
• Route getAccountAssetByID, getAccountAssetsByIDs, getAccountAssets, fetchAssetsAndBalancesForAccount, and saveMany through Core when migration is active
• When migration is on, fetch returns only snap-owned assets; save publishes them via keyring events without local persistence

Part of WPN-1497. Stack:

1. refactor(tron-wallet-snap): extract shared asset utils and inject SnapAssetsAdapter #143
2. feat(tron-wallet-snap): add CoreAssetsAdapter and mapControllerAsset #144
3. feat(tron-wallet-snap): route asset reads through Core when migration is on #145 (this PR)

Replaces outdated #127 / #141.

Test plan

• yarn workspace @metamask/tron-wallet-snap run build
• yarn workspace @metamask/tron-wallet-snap run jest --no-coverage src/services/assets/AssetsService.test.ts
• With migration flag off: asset reads/writes/fetch behave as Snap-only
• With migration flag on: fungible reads come from AssetsController; fetch returns only snap-owned assets; saveMany emits only snap-owned assets and does not persist fungibles locally

[ulissesferreira]

Reopening to re-trigger CI after amend