fetch both selectedcurrency and usd prices

[bergarces]

Explanation

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
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Medium Risk
Medium risk because it changes the AssetPrice/FungibleAssetPrice type shape (adds assetPriceType/usdPrice and narrows the union), which may be breaking for downstream consumers, and it increases Price API usage by fetching USD in addition to the selected currency.

Overview
Price fetching now queries the spot-prices API for both the selected currency and USD (in parallel when needed) and returns a normalized assetsPrice map that includes price (selected currency), usdPrice, lastUpdated, and assetPriceType: 'fungible'.

Types were updated to make prices a discriminated union (assetPriceType), factor shared fields into BaseAssetPrice, add usdPrice to FungibleAssetPrice, and narrow AssetPrice to FungibleAssetPrice | NFTAssetPrice.

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[bergarces]

Moved the logic that validates the result from the API here and added an extra check to verify that the USD price is also there.

This also allows us to remove this logic from the two places that were calling this private method.

[bergarces]

I have made some minor adjustment to this type, which also addresses this TODO I added to the client (https://github.com/MetaMask/metamask-extension/blob/main/shared/modules/selectors/assets-migration.ts#L715).

It's very convenient to have a type discriminator field with unions of very different types, as that allows typescript to to perform type guards easily.

For that reason, I added an assetPriceType with a specific value for each type and removed the generic (BaseAssetPrice & { [key: string]: Json }), as it is not used anywhere and it's unlikely it'll ever be needed. If it ever is needed, we can add it then and create a new type for it.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[bergarces]

Make all the price types extend this one, which is the absolutely bare minimum needed.