Pick image_proxy changes from searxng (#2965)

* [mod] /image_proxy: don't decompress images

* [fix] image_proxy: always close the httpx respone

previously, when the content type was not an image and some other error,
the httpx response was not closed

* [mod] /image_proxy: use HTTP/1 instead of HTTP/2

httpx: HTTP/2 is slow when a lot data is downloaded.
https://github.com/dalf/pyhttp-benchmark



also, the usage of HTTP/1 decreases the load average

* [mod] searx.utils.dict_subset: rewrite with comprehension

Co-authored-by: Alexandre Flament <alex@al-f.net>