docs: Switchable toml code snippets

[HARSHVARANDANI]

Description

This PR adds switchable pixi.toml / pyproject.toml code snippets across the documentation where only pixi.toml examples were previously shown.

The changes convert relevant manifest examples to also include their pyproject.toml equivalents (using the tool.pixi.* namespace where applicable) and present them using tabbed code blocks for easier comparison. Sections where the configuration is identical (e.g., [package.*] blocks) or where the content belongs to Pixi configuration rather than the project manifest were left unchanged.

This improves clarity for users who prefer using pyproject.toml while keeping existing pixi.toml examples intact.

Before

After

Fixes #4452

These changes only affect the documentation, so there are no dedicated tests for this functionality.

To verify the changes locally:

Run the documentation site locally:

pixi run docs

Open the generated documentation in the browser and verify that the new pixi.toml / pyproject.toml tabbed code blocks render correctly.

Checklist:

• I have made corresponding changes to the documentation