The yfinance_news module was missing the yf_retry exponential backoff
wrapper that y_finance.py and stockstats_utils.py already use. When
Yahoo Finance returns HTTP 429 (Too Many Requests), get_news_yfinance
and get_global_news_yfinance would fail immediately instead of retrying.
This adds yf_retry around:
- stock.get_news() in get_news_yfinance()
- yf.Search() in get_global_news_yfinance()
Fixes#437