[fast_inference] Make API Great Again And Again (#923)

* 为fast_inference分支适配新的WebAPI

* modified:   api_v2.py

* 修改文档细节

* modified:   api_v2.py

* 优化了代码逻辑，提升健壮性

* 修改文档细节

* 修改文档细节

* 优化代码逻辑

* 修改注释细节

GPT_SoVITS/TTS_infer_pack/text_segmentation_method.py

@@ -16,6 +16,9 @@ def get_method(name:str)->Callable:
         raise ValueError(f"Method {name} not found")
     return method
 
+def get_method_names()->list:
+    return list(METHODS.keys())
+
 def register_method(name):
     def decorator(func):
         METHODS[name] = func