More metafield type conversions for imports

Altera already converts many metafield types automatically during import - things like booleans, colors, dates, money, measurements, and rich text. This update extends that support to cover more types.

Improvements

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• Link metafields - Plain URLs like https://example.com are now converted to Shopify’s required JSON format with url and text keys.
• Rating metafields - Plain numbers like 4.5 are now wrapped with the correct scale values from your metafield definition.
• List types - List variants of link and color types are now converted automatically.
• Metaobject fields - Metaobject imports now use the same conversion logic as product metafields, so all type conversions work consistently across both.