server : support multi-modal context checkpoints (#19849)
* Modify llama-memory-hybrid-iswa.cpp
* Modify llama-memory-recurrent.cpp
* Modify server-common.cpp
* Modify server-common.h
* Modify server-context.cpp
* Modify server-task.h
* Added comment to llama-memory-hybrid-iswa.cpp
* Remove comment from server-context.cpp
* Stylistic fix server-context.cpp
* Fix an issue when seqrm isn't called in server-context.cpp
* cont : alternative impl
* cont : cleanup
* cont : n_tokens -> int64_t
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Co-authored-by: timkhronos <timkhronos@gmail.com>
