rpc: include nb in the get_alloc_size cache key and floor the result at ggml_nbytes (llama/29283)
* rpc : include nb in the get_alloc_size cache key and floor the result at ggml_nbytes
* cont : remove redundant comment
* cont : add TODO
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>