Improve G2PWPinyin model handling

- Add 'bert_pretrained_dir' environment variable as the highest priority for model_source
- Replace redundant g2pw initialization in chinese2.py with import from download.py
- Remove unused 'parent_directory' variable

GPT_SoVITS/download.py

@@ -7,7 +7,7 @@ from text.g2pw import G2PWPinyin
 
 g2pw = G2PWPinyin(
     model_dir="GPT_SoVITS/text/G2PWModel",
-    model_source="GPT_SoVITS/pretrained_models/chinese-roberta-wwm-ext-large",
+    model_source=os.environ.get("bert_pretrained_dir") or os.environ.get("bert_path") or "GPT_SoVITS/pretrained_models/chinese-roberta-wwm-ext-large",
     v_to_u=False,
     neutral_tone_with_five=True,
 )

GPT_SoVITS/text/chinese2.py

@@ -28,15 +28,8 @@ import jieba_fast.posseg as psg
 is_g2pw = True  # True if is_g2pw_str.lower() == 'true' else False
 if is_g2pw:
     # print("当前使用g2pw进行拼音推理")
-    from text.g2pw import G2PWPinyin, correct_pronunciation
-
-    parent_directory = os.path.dirname(current_file_path)
-    g2pw = G2PWPinyin(
-        model_dir="GPT_SoVITS/text/G2PWModel",
-        model_source=os.environ.get("bert_path", "GPT_SoVITS/pretrained_models/chinese-roberta-wwm-ext-large"),
-        v_to_u=False,
-        neutral_tone_with_five=True,
-    )
+    from text.g2pw import correct_pronunciation
+    from download import g2pw
 
 rep_map = {
     "：": ",",