fix: add explicit UTF-8 encoding to file operations for Windows compatibility (#1845)

On Windows, Python's default encoding is the system locale (e.g., cp1252,
gbk) rather than UTF-8. This causes UnicodeDecodeError when reading
sdkconfig files, CMakeLists.txt, or JSON configs that contain non-ASCII
characters (e.g., Chinese comments, UTF-8 BOM).

Fix: Add explicit encoding='utf-8' to all text file open() calls in:
- scripts/release.py (Path.open() for config.json, CMakeLists.txt, sdkconfig)
- scripts/build_default_assets.py (io.open() for sdkconfig, open() for headers/configs)
- scripts/versions.py (open() for info.json read/write)

Relates to #1792

Co-authored-by: Nicola Spieser <redbasecap@users.noreply.github.com>

scripts/versions.py

@@ -236,11 +236,11 @@ def main():
                 target_dir = os.path.join("firmwares", tag)
                 info["tag"] = tag
                 info["url"] = os.path.join(os.environ['OSS_BUCKET_URL'], target_dir, "xiaozhi.bin")
-                open(info_path, "w").write(json.dumps(info, indent=4))
+                open(info_path, "w", encoding="utf-8").write(json.dumps(info, indent=4))
                 # upload all file to oss
                 upload_dir_to_oss(folder, target_dir)
                 # read info.json
-                info = json.load(open(info_path))
+                info = json.load(open(info_path, encoding="utf-8"))
                 # post info.json to server
                 post_info_to_server(info)