[Performance] Optimize rejectGeneratedStaticAssets filtering

[gonzaloriestra]

Why is this change necessary?

In packages/theme/src/cli/utilities/asset-checksum.ts, rejectGeneratedStaticAssets constructed liquidAssetKeys using chained .filter(...) and .map(...) array operations. This created two temporary intermediate arrays and traversed the theme checksum array twice.

How was it resolved?

Replaced the .filter(...).map(...) chaining with a single for...of loop that directly inserts matching Liquid asset keys into the Set. This avoids extra array allocations and reduces iteration overhead when processing large theme checksum sets during theme operations (e.g., theme pull or theme push).

How to test your changes?

shopify theme pull or shopify theme push

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PR created automatically by Jules for task 8883107987903545011 started by @gonzaloriestra

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