ZM25XC

Change default encoding to utf-8 in `normalize_header_key` and `normalize_header_value` functions

5

#### Description I have encountered decoding errors with some requests that use ASCII encoding. Changing the default encoding to UTF-8 resolves these errors. I propose updating the `normalize_header_key` and `normalize_header_value`...

# Summary This Pull Request addresses the issue of decoding errors encountered when using ASCII encoding in the `normalize_header_key` and `normalize_header_value` functions in `_utils.py`. By changing the default encoding to...