feat: add option for text stroke width

[Cly1st]

• Added an option stroke_width in CorpusCfg to allow adding stroke width to text.
• Included usage example in effect_layout_example.py and sample output image in effect_layout_image.

[Cly1st]

I’m looking for a simple add a stroke to the text. However, it seems this PR might conflict with the existing TextBorder.
Please confirm if there’s a conflict? Thank you!

[scyyh11]

Sorry for the late response.

Thank you for the contribution — adding stroke support will be useful for generating richer, more legible text renders. The purpose of such an implementation is to provide a visual transformation, which aligns more with the concept of an effect. CorpusCfg is generally intended for corpus-level defaults (like font, spacing, or language settings), while visual styling features such as stroke or outline fit better in the effect pipeline. What do you think about moving this logic into an effect for better composability and consistency? Open to discussion!