[Bug]: Python Enrichment BigQuery handler does not expose `max_batch_duration_secs` to `BatchElements`

What happened?

Description: In Python Enrichment, RequestResponseIO supports passing batching kwargs from Caller.batch_elements_kwargs() into BatchElements(**kwargs).

BatchElements supports max_batch_duration_secs, but BigQueryEnrichmentHandler currently only sets:

• min_batch_size
• max_batch_size

As a result, users of BigQueryEnrichmentHandler cannot configure max_batch_duration_secs, even though the downstream batching transform supports it.

Code path: BigQueryEnrichmentHandler -> Enrichment -> RequestResponseIO -> BatchElements

Current behavior max_batch_duration_secs is not available/configurable from BigQueryEnrichmentHandler and therefore is never forwarded to BatchElements.

Expected behavior BigQueryEnrichmentHandler should optionally accept max_batch_duration_secs and pass it through batch_elements_kwargs() when batching is enabled.

Proposed fix

1. Add optional max_batch_duration_secs: Optional[float] = None to BigQueryEnrichmentHandler.__init__.
2. When query_fn is not used, include it in _batching_kwargs (when provided).

Additional note: CloudSQLEnrichmentHandler appears to have the same batching-kwargs limitation and may benefit from parity in a follow-up or same PR.

Issue Priority

Priority: 2 (default / most bugs should be filed as P2)

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