Add explanation notice for modern image format settings

[reverb256]

Summary

Fixes #2442

Users frequently open support topics confused about why their uploads aren't generating AVIF/WebP files. The plugin discards converted files if they're larger than the original (webp_uploads_discard_larger_generated_images defaults to true), but there was no explanation in the admin dashboard.

Changes

• Replaced __return_empty_string section callback with webp_uploads_render_settings_section_info() which renders an informational notice in the Modern Image Formats settings section
• The notice explains why modern format images may not always be generated
• Links to the existing plugin FAQ on wordpress.org for full details
• Follows the existing notice notice-info inline pattern used in other setting callbacks in this file

Screenshots

The notice appears at the top of the Modern Image Formats settings section, before the output format dropdown:

ℹ️ Modern image formats (e.g. WebP, AVIF) are only generated when they result in a smaller file than the original. If a converted image would be larger, the original is kept instead. For more details, see the FAQ.

Testing

• php -l — no syntax errors
• phpcs --standard=WordPress-Core — zero violations
• phpstan analyse — no errors

AI Disclosure

AI tooling (Claude) was used to assist with code generation and analysis. The code was reviewed, tested, and validated manually.

[github-actions]

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Co-authored-by: westonruter <westonruter@git.wordpress.org>
Co-authored-by: b1ink0 <b1ink0@git.wordpress.org>

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[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.38%. Comparing base (61b1379) to head (adf158f).

Files with missing lines	Patch %	Lines
plugins/webp-uploads/settings.php	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk    #2443      +/-   ##
==========================================
+ Coverage   69.33%   69.38%   +0.05%     
==========================================
  Files          90       90              
  Lines        7749     7762      +13     
==========================================
+ Hits         5373     5386      +13     
  Misses       2376     2376              

Flag	Coverage Δ
multisite	69.38% <92.85%> (+0.05%)	⬆️
single	35.84% <92.85%> (+0.10%)	⬆️

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