minor : add const qualifiers (#2853)
* made the methods const
# Conflicts:
# examples/convert-llama2c-to-ggml/convert-llama2c-to-ggml.cpp
* made method const
* Update convert-llama2c-to-ggml.cpp
removed write_raw and write_u32
* llama2c : remove misleading const
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Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>
