perf(multichain): batch OnAsset* requests

[danroc]

Explanation

Currently, OnAssetConversion and OnAssetMarketData requests are batched per account, which can lead to duplicate requests when an asset is present in multiple accounts.

This PR resolves this issue by batching the requests per Snap for all assets managed by each Snap.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed, highlighting breaking changes as necessary
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

---

Note

Batch OnAssetsConversion and OnAssetsMarketData per Snap across accounts with deduplicated assets; refactor controller, update tests, and note in changelog.

• MultichainAssetsRatesController:
  • Batch requests per Snap by aggregating assets across non‑EVM accounts via #addAssetsToSnapIdMap, deduplicating assets before calling Snaps.
  • New helpers to fetch data: #getConversionRates, #getMarketData, and consolidated #getUpdatedRatesFor combining both; added #getCaipCurrentCurrency.
  • Refactor #handleSnapRequest with typed overloads; state merge via #applyUpdatedRates now keyed by CaipAssetType.
  • updateAssetsRates and #updateAssetsRatesForNewAssets now build a Snap‑ID→assets map and issue a single batched call per Snap.
• Tests:
  • Update to reflect batched behavior and CAIP currency keys (swift:0/iso4217:USD); add multi‑Snap scenarios and revised spies/mocks.
• Changelog:
  • Note batching of OnAssetConversion and OnAssetsMarketData requests to non‑EVM account Snaps.

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[danroc]

@metamaskbot publish-preview

[FrederikBolding]

Maybe simpler to construct the Snap ID -> Asset List mapping here instead of constructing this mapping and then constructing the reverse mapping in the next function call?

[danroc]

I did in two steps mainly because it also dedupes the assets. If I build the snapId -> assets[] mapping here I need to do another pass to remove the deplicates of each entry.

[FrederikBolding]

We could use a Snap ID -> Asset Set for that perhaps? Up to you!

[FrederikBolding]

Should we keep this? So we don't create sets for Snaps that don't have any assets

[danroc]

Indeed, I added some checks to prevent adding empty sets to the map, or calling the Snap when the list of assets is empty.