This fix addresses a fork-safety issue that caused the Feast feature
server to crash when launched with multiple Gunicorn workers and a
SQL Registry backend.

Root Cause:
- SQLAlchemy's connection pools are not fork-safe
- Background refresh threads inherited from parent become invalid
- Forked workers share corrupted connection pool state

Solution:
- Add `on_worker_init()` hook to BaseRegistry for post-fork cleanup
- Add `reinitialize_engines()` to SqlRegistry for engine disposal/recreation
- Implement Gunicorn `post_fork` hook in FeastServeApplication
- Each worker now properly reinitializes DB connections after fork

Changes:
- sdk/python/feast/infra/registry/base_registry.py: Add on_worker_init()
- sdk/python/feast/infra/registry/caching_registry.py: Override to restart refresh thread
- sdk/python/feast/infra/registry/sql.py: Add reinitialize_engines() and on_worker_init()
- sdk/python/feast/feature_server.py: Add post_fork hook to Gunicorn app

Fixes: feast-dev#5784

…dev#5597)

This adds support for configuring DuckDB's HTTPFS extension S3 settings,
enabling compatibility with S3-compatible storage providers like MinIO,
LocalStack, and other providers that require path-style URLs.

New configuration options in DuckDBOfflineStoreConfig:
- s3_url_style: 'path' or 'vhost' - URL style for S3 requests
- s3_endpoint: Custom S3 endpoint URL
- s3_access_key_id: AWS access key ID
- s3_secret_access_key: AWS secret access key
- s3_region: AWS region
- s3_use_ssl: Whether to use SSL for S3 connections

Example usage in feature_store.yaml:
```yaml
offline_store:
    type: duckdb
    s3_url_style: path
    s3_endpoint: localhost:9000
    s3_access_key_id: minioadmin
    s3_secret_access_key: minioadmin
    s3_region: us-east-1
    s3_use_ssl: false
```

Implementation details:
- S3 configuration is applied via DuckDB's HTTPFS extension
- Settings are cached to avoid reconfiguring on each operation
- Graceful error handling if configuration fails
- Type validation ensures only valid values are accepted

Fixes: feast-dev#5597