Improve retry configuration and remove yfinance dependency

[shackmann]

Note

Low Risk
Changes are limited to default transport retry behavior and optional notebook packaging; no auth or API contract changes.

Overview
HTTP retry defaults are tuned for DataRobot deployments: max_attempts goes from 10 to 20, and 470 is added to the retriable status codes so the client can wait through custom-model stop/warm-up windows after a deployment restart. The same values appear in RetryConfig, config.sample.yaml, and the README transport example.

The notebooks optional extra no longer pulls in yfinance—only pandas remains. forecast_trading.ipynb (Yahoo Finance / Kelly trading demo) is removed, and tests/test_notebooks.py no longer expects that notebook in the catalog. uv.lock is refreshed to drop the yfinance dependency tree.

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