server: improve speed of speculative decoding (#17808)
* server: improve speed of speculative decoding
* fix small draft case
* add link to the PR
* server : fix generation time measurement
* server : fix draft acceptance logs (add SRV_CNT, SLT_CNT macros)
* server : add comment
* add PR to docs
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
