Model stats calculator

[odashi]

Add a script calculate_model_stats.py that reads a Megatron-LM checkpoint and calculates some statistics of containing weights:

• Shape
• min/max/sum of $n$-th power of values ($n=1,2,3,4$)
• min/max/sum of $n$-th power of absolute values ($n=1,2,3,4$)

[hkiyomaru]

LGTMです．綺麗なコードですね．Usage に書いてある通りに実行してみて，ちゃんと動いたら approve 出します．