perf(utils): optimized reducer to avoid creating new objects

[Connormiha]

Description

Rewrote reducer to avoid creating a new object on each iteration and prevent O(n²) complexity.

Resolves #issue-number

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[AriPerkkio]

Looks good. We should probably check other parts of the codebase for similar improvements.

I've seen this kind of reduce mutation change improve perf in another private repo before. 👍