Partition Mutable Buffer as Core ML State (#5165)

* partition mutable buffer to coreml state

* delegate llama mutable buffer to coreml

* fix lint

* support embedding quantize

* try fix CI: 1. pin coremltools 8.0b2; 2. refrain from defaulting stateful llama until CI machine upgraded to MacOS 15

* address review comments: 1. add arg help info; 2. add mutable buffer partition log

* fix CI: executorch example model test env is using older transformers, that does not support numpy 2.0

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Co-authored-by: yifan_shen3 <yifan_shen3@apple.com>