[Hubs] Fix ingestion OOM errors by eliminating strcat() in emptiness checks

[Copilot]

Costs_transform_v1_0 and Costs_transform_v1_2 were hitting E_LOW_MEMORY_CONDITION during Data Factory pipeline ingestion due to unnecessary string allocation from using strcat() purely as an emptiness guard.

Changes

• IngestionSetup_v1_0.kql / IngestionSetup_v1_2.kql: Replace the single strcat()-based check with individual isnotempty() predicates in the "populate missing prices" filter:

// Before — allocates a concatenated string just to check emptiness
and isnotempty(strcat(x_SkuMeterId, x_SkuOfferId))

// After — no allocation; also correctly requires both fields (matches the comment intent)
and isnotempty(x_SkuMeterId) and isnotempty(x_SkuOfferId)

The old form is semantically looser (true if either field is non-empty), while the price lookup key tmp_ReservationPriceLookupKey requires both — so the corrected form is also more precise. All other strcat() usages in these files are legitimate string construction and were left unchanged.