Fix UnicodeDecodeError reading model_config.yaml on Windows

build_sortformer opened the extracted NeMo model_config.yaml without an
explicit encoding, so on Windows Python used the cp1252 (charmap) codec and
raised UnicodeDecodeError on UTF-8 bytes in the file. Read it as UTF-8.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Mason Corey <masoncorey@microsoft.com>

Author: themason2011

src/mobius/models/sortformer.py

@@ -715,7 +715,7 @@ def build_sortformer(
         extract_dir = tmp.name
 
     try:
-        with open(os.path.join(extract_dir, "model_config.yaml")) as f:
+        with open(os.path.join(extract_dir, "model_config.yaml"), encoding="utf-8") as f:
             yaml_cfg = yaml.safe_load(f)
         state_dict = torch.load(
             os.path.join(extract_dir, "model_weights.ckpt"),