Gguf dump start data offset via --data-offset and some extra refactor (#8054)
* gguf-dump: add --data-offset
* gguf-dump: add tensor data offset table
* gguf-dump: refactor GGUFReader for clarity
* gguf-dump: add --data-alignment
* gguf-dump.py: Rename variables and adjust comments
start_data_offset --> data_offset
_build_tensors_info_fields --> _build_tensor_info