Disable network_alpha option if not specified

It's exactly the title.
If user has not used the 'network_alpha' option param, please disable function to regist 'alpha' to safetensor, and do not scale learning.

or, please provide additional options that do not use network_alpha at all (do not use LORA scale, do not regist alpha).

ご苦労様です。
タイトル通りの内容です。

最近追加されたnetwork_alphaオプションの意図は十分理解できますが、それを望まない人もいます。
network_alpha機能を無効にするオプションの追加をお願いします。 （学習率のスケーリングとsafetensorにalpha記載を無効に）

No files or tests are named. Trace how the network_alpha option controls learning-rate scaling and alpha serialization in safetensor output, then determine how an omitted option should differ from an explicitly configured value. Done means omitted network_alpha avoids both scaling and alpha registration while existing behavior remains available.

Written by the indexing model from the issue text.