Is your feature request related to a problem? Please describe.
Currently, RustFS does not support the If-None-Match HTTP header for conditional GET requests. This prevents clients from efficiently checking if an object has changed, resulting in unnecessary downloads and wasted bandwidth.

Describe the solution you'd like
Add support for the If-None-Match header so that RustFS can respond with 304 Not Modified when the object's ETag matches. This would improve caching efficiency and compatibility with S3 clients that rely on ETag validation.

Describe alternatives you've considered
There is no practical alternative: conditional GET based on ETag requires server-side support.

Additional context
https://docs.aws.amazon.com/AmazonS3/latest/API/API_GetObject.html#API_GetObject_RequestSyntax