cleanup indexer transform function (kkrt-labs#1226)

* - Changed return statements to array filters
- Moved object mutations from map to forEach

* Address comments:
- Add name constants for Collection
- cleanup

* Fix typing

* Divide transform into helper functions for clarity

* fix: fmt and type

* fix: tests

* fix: refactoring

* fix: remove update store

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Co-authored-by: Eugenio Paluello <[email protected]>