docs: clarify LineWidth enum non-sequential style numbering

[palewire]

Improve documentation for LineWidth enum to highlight that style numbers
do not correspond to line thickness in sequential order. Added warnings
and examples to prevent confusion where style3 is the thinnest (1px) and
style2 is the thickest (4px), contrary to what the numbering suggests.

Changes:

• Enhanced docstring with clear attribute descriptions and warnings
• Added inline comments on enum values showing pixel widths
• Expanded Field description with concrete examples
• Emphasized using enum values over raw strings to avoid confusion

This addresses potential developer confusion when using raw API values
where higher style numbers don't mean thicker lines.

[Copilot]

Pull Request Overview

This PR enhances the documentation for the LineWidth enum to clearly warn users that the style numbers (style0-style3) don't increase with thickness, which is counterintuitive. The documentation is updated in both the enum definition and the Field description to prevent confusion.

• Updated LineWidth enum docstring with warnings and clearer examples
• Expanded Field description with inline examples and warnings about non-sequential style numbers
• Added inline comments to enum values highlighting the counterintuitive numbering

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
datawrapper/charts/enums/line_width.py	Enhanced enum docstring with warnings, restructured attributes section, and added inline comments to enum values
datawrapper/charts/line.py	Expanded Field description with examples and warning about style number ordering

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