Fix yfinance-proxy client initialization

[google-labs-jules]

The api-scraper was attempting to start a defunct Python-based yfinance-proxy when run with the --yahoo flag. This change updates the NewYahooProxyClient function to use the Go-based YahooFinanceClient, which directly queries the Yahoo Finance API. This resolves the test failures caused by the "connection refused" and "401 Unauthorized" errors. The call to proxyCl.Stop() was also removed from main.go as it is no longer needed.

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PR created automatically by Jules for task 2406160525467598296 started by @hunterjsb

[google-labs-jules]

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