Docs: Expand preview style features documentation with examples (#4987)

* Docs: Expand preview style features documentation with examples

Adds detailed descriptions and code examples for preview style features
that previously only had single-line descriptions, addressing issue #4429.

Changes:
- Add dedicated section for `wrap_comprehension_in` feature:
  - Explanation of when and why comprehensions are wrapped
  - Examples with list comprehensions
  - Examples with dictionary comprehensions

- Add dedicated section for `simplify_power_operator_hugging` feature:
  - Explanation of power operator whitespace handling
  - Examples with simple expressions
  - Examples with split expressions

- Updated feature list to link to the new detailed sections

This brings the preview features documentation in line with the unstable
features documentation style, which already includes detailed sections
and examples for each feature.

Fixes #4429

* Add changelog entry for preview style docs expansion (#4987)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix power operator example per review

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>