Refactor: when pyopenjtalk_worker is called without initialization, continue processing without a worker

When using style-bert-vits2 as a library, the requirement to be able to launch it in multiple processes may not be necessary. Also, if the library is embedded and exe-ed using PyInstaller or similar, it is difficult to make pyopenjtalk_worker run in a separate process.
Therefore, we changed it so that the worker is used only when it is explicitly initialized.

server_fastapi.py

@@ -43,7 +43,7 @@ ln = config.server_config.language
 
 # pyopenjtalk_worker を起動
 ## pyopenjtalk_worker は TCP ソケットサーバーのため、ここで起動する
-pyopenjtalk.initialize()
+pyopenjtalk.initialize_worker()
 
 # 事前に BERT モデル/トークナイザーをロードしておく
 ## ここでロードしなくても必要になった際に自動ロードされるが、時間がかかるため事前にロードしておいた方が体験が良い