server : host-memory prompt caching (#16391)

server : host-memory prompt caching (#16391)

* minor : code style

* server : fix prompt similarity calculation

* server : initial host-memory prompt caching

* cont

* server : refactor

* cont

* cont : make the server task of the slot const

* cont : minor [no ci]

* server : cache prompts and checkpoints only for completion tasks

* server : improve prompt caching logic

* cont : fix check for number of cached prompts [no ci]

* server : improve caching logic, add -cram CLI arg

* server : print prompt mismatch info

* cont : better naming [no ci]

* server : improve prompt cache loading logic

* server : add option to debug the slot contents (#16482)

* server : add option to debug the slot contents

* Update tools/server/server.cpp

---------

Co-authored-by: Xuan-Son Nguyen <redacted>
* server : add option to disable prompt cache

---------

Co-authored-by: Xuan-Son Nguyen <redacted>