ggml: add graph_reused (#21764)
* ggml: add graph_reused
* use versioning instead of reuse flag
* increment version with atomic
* use top bits for split numbering
* add assert
* move counter to ggml.c
* set uid in split_graph only
* fix windows
* address further review comments
* get next_uid rather than doing bit manipulation
* rename + add comment about uid
