kv-cache: Fix state restore fragmented cache (#17982)

kv-cache: Fix state restore fragmented cache (#17982)

* kv-cache : fix state restore with fragmented cache (#17527)

Change find_slot to allow non-contiguous allocation during state restore. Fixes 'failed to find available cells in kv cache' error when restoring state to fragmented cache.

* tests : update logic

* cleanup: tightened state_read_meta sig, added is_contiguous case

* fix: state_read_meta arg reorder loose ends

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Co-authored-by: Georgi Gerganov <redacted>