feat: Add automatic credential refresh for S3 storage operations

[rdheekonda]

Key Changes:

• Implement automatic credential refresh system for AWS S3 storage

• Add decorator pattern for clean retry logic across storage operations

• Configure default 4 hours credential lifetime with 5-minute refresh buffer

• Prevent authentication failures during long-running artifact uploads

Added:

• storage_utils.py with @with_credential_refresh decorator
• _refresh_credentials_if_needed() method to RunSpan class
• docstring-parser development dependency for documentation
• Auto-generated MDX documentation for new functionality
• Constants: DEFAULT_FS_CREDENTIAL_DURATION ` to 14400s
• FS_CREDENTIAL_REFRESH_BUFFER to 300 secs

Changed:

• RunSpan._store_file_by_hash() to use credential refresh decorator
• ArtifactStorage.store_file() to support credential refresh callbacks
• ApiClient to handle configurable credential duration parameter

Testing:

✅ Tested with forced credential expiry (immediate refresh)
✅ Tested with natural 15-minute expiry cycle
✅ Verified refresh logs appear: "Refreshing storage credentials"
✅ Confirmed artifact upload during credential transitions

This coordinates with the platform PR to support configurable credential duration on the /user-data/credentials endpoint.