docs: document Syntax.stylize_range with working examples

[wenlongcai1995]

Summary

This PR documents the Syntax.stylize_range method, which allows users to apply custom styling to specific portions of syntax-highlighted code.

Changes

• docs/source/syntax.rst: Added "Stylize Range" section with usage examples showing line/column indexing conventions (1-based lines, 0-based columns)
• examples/sintaxy_with_styles.py: Working demonstration script

Closes #2842

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• Links to the issue ([REQUEST] Document Syntax.stylize_range #2842) where a solution has been approved by @willmcgugan ✓

[RedEye1605]

Nice documentation addition! stylize_range is a useful but underdocumented feature, so this is a great contribution.

A few thoughts:

• Typo in filename: The example file is named sintaxy_with_styles.py — should be syntax_with_styles.py. This is also referenced in the docs at the bottom of the new section.
• The two example snippets in the .rst and the .py file overlap quite a bit. Consider keeping the doc example minimal and letting the standalone .py file be the comprehensive demo, or vice versa — reduces maintenance burden if the API changes.
• The .. note:: about line numbers is a helpful touch.

Thanks for documenting this!