Chore(): localised improvement to promotion module (#13446)

**What**
- Remove overserialization withing transaction and rely more on internal service or protected method instead which does not serialize and work with Infered entity type
- Slightly rework loop complexity

Overall, this gives a good spare of resources and time spent for serialization

.changeset/smart-numbers-build.md

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+"@medusajs/promotion": patch
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+Chore/localised improvement to promotion module