* fix(s3): add retry with exponential backoff for transient S3 503/500 errors
S3 occasionally returns 503 "Slow Down" during PUT operations when
request rates spike above partition limits. The current code makes a
single upload attempt via httpx — unlike boto3, httpx has no built-in
retry for transient S3 errors. Failed uploads permanently lose the
request's audit/logging data.
Add exponential backoff retry (3 attempts, 1s/2s delays) for S3
500/503 responses in both async_upload_data_to_s3 and
upload_data_to_s3. Logs a warning on each retry with the S3 object
key for observability.
In production we observed ~18 permanent S3 upload failures per day
(124 over 7 days) — all transient 503s that would have succeeded on
a single retry.
* test(s3): add unit tests for S3 upload retry logic
Tests cover:
- Async retry on 503 (succeeds on second attempt)
- Async retry on 500
- Exhausted retries on persistent 503 (calls handle_callback_failure)
- No retry on 4xx errors (403)
- Sync retry on 503
* style(s3): move time import to module level
Address review feedback: move `import time` from inside
upload_data_to_s3 to the top-level imports per project style guide.
Add s3_use_virtual_hosted_style parameter to support AWS S3 virtual-hosted-style URL format (bucket.endpoint/key) alongside the existing path-style format (endpoint/bucket/key).
This enables compatibility with S3-compatible services like MinIO and aligns with AWS S3 official terminology.
