Update RP-1311 Python examples and quick start

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Summary

Update the Python documentation examples to match the current CEA API and canonical RP-1311 samples.

Changes

• Replace obsolete byte-string species names with strings in Examples 1–14
• Fix broken Example 3 indentation and missing Example 11 inputs
• Update sample paths and related prose
• Add a working H2/O2 HP combustion quick-start example

Testing

• make -C docs html
• Executed the quick-start example successfully

Compatibility / Numerical behavior

• No expected changes to numerical results
• Expected changes (explain and provide validation)