fix: handle zero values for max_retries, initial_backoff, and max_backoff in OpenSearch index_documents

[hsusul]

Description

Fixes an issue in awswrangler.opensearch.index_documents where passing 0 for retry and backoff configuration arguments (max_retries=0, initial_backoff=0, max_backoff=0) resulted in incorrect default fallback assignment and validation bypass.

Root Cause

1. if use_threads and any([max_retries, initial_backoff, max_backoff]): evaluated any([0, None, None]) as False because 0 is falsey in Python. As a result, passing max_retries=0 when use_threads=True failed to trigger exceptions.InvalidArgumentCombination.
2. When use_threads=False, bulk_kwargs["max_retries"] = 5 if not max_retries else max_retries evaluated not 0 as True, overriding max_retries=0 to 5. Similarly, initial_backoff=0 was overridden to 2 and max_backoff=0 was overridden to 600.

Solution

• Updated the use_threads validation check to any(x is not None for x in (max_retries, initial_backoff, max_backoff)) to properly check for explicit argument presence.
• Updated default bulk_kwargs assignments to check x is None instead of not x, ensuring explicit zero values (0) are preserved.
• Added unit tests with mocked OpenSearch clients to verify both unthreaded zero-value propagation and threaded exception raising.

Validation Results

• poetry run pytest tests/unit/test_opensearch.py -k "test_index_documents_zero_retries" passed cleanly.
• poetry run pytest tests/unit/test_moto.py passed cleanly (46 passed).
• poetry run ruff check and poetry run ruff format --check passed cleanly.

AWS Integration Tests Not Run

• Tests in tests/unit/test_opensearch.py requiring live AWS OpenSearch domain infrastructure were not run as they require live AWS credentials and CloudFormation stack resources.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.