[GITHUBTANMAY2003]

Description

S3 Vectors errors currently reach users as low-level Botocore ClientError exceptions. This PR translates the common not-found, access-denied, and validation failures into dynavec exceptions that are easier for applications to handle.

Related issue

Fixes #15

Changes

• Added AccessDeniedError and ValidationError, alongside the existing NotFoundError.
• Added a shared error translator used by both the synchronous and asynchronous S3 Vectors stores.
• Covered direct requests, paginated operations, and concurrent uploads.
• Kept unknown and temporary AWS errors unchanged so the existing retry logic continues to work.
• Added offline tests for error mapping, retries, pagination, and concurrent failures.

Testing

• 107 affected tests passed, including 56 new error-handling tests
• Ruff passed
• Mypy passed
• Full suite passed locally with the OpenAI import-order workaround
• Documentation update not required.