fix(AssetControllers): assetMetadata undefined unit

[Kriys94]

Explanation

This fixes when assetMetadata.units is undefined

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

Fixes selector crash for missing metadata

• Update selectAllMultichainAssets to use assetMetadata.units?.find(...), avoiding crashes when units is absent in asset metadata
• Add corresponding entry under Fixed in CHANGELOG.md

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