server, ui : Add support for HTTP ETags in llama-server (#23701)
* allow caching of ui elements in llama-server
* use fnv_hash
* Update tools/server/server-http.cpp
etag has to be set always
Co-authored-by: Xuan-Son Nguyen <thichthat@gmail.com>
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Co-authored-by: Xuan-Son Nguyen <thichthat@gmail.com>