Batch requests were not recording latency in the
lava_provider_request_latency_per_function metric because GetRawRequestHash() intentionally returns WontCalculateBatchHash for batches, causing the code to break early and return emptyTime (0ms).

This fix detects batch requests explicitly and returns immediately with the actual latency, while preserving the original retry behavior for single requests that fail to hash unexpectedly.

Description

Closes: #XXXX

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