Add Adanos market sentiment event study example

[alexander-schneider]

Summary

• add an optional Adanos Market Sentiment API example that turns Reddit stock buzz days into a simple finmarketpy event study
• keep the example runnable without credentials by falling back to sample sentiment and price data
• document the example in the README and cover the fallback/date-window/event-study helpers with tests

Checks

• python -m py_compile finmarketpy_examples/adanos_market_sentiment_example.py tests/test_adanos_market_sentiment_example.py
• uv run ruff check finmarketpy_examples/adanos_market_sentiment_example.py tests/test_adanos_market_sentiment_example.py
• uv run python -m pytest tests/test_adanos_market_sentiment_example.py -q
• .venv/bin/python -m pytest tests/ -q
• uv run python finmarketpy_examples/adanos_market_sentiment_example.py

The live Adanos path uses explicit from/to UTC date windows and only requires ADANOS_API_KEY; plotting is opt-in with ADANOS_PLOT=1 so the sample path works in headless environments.