Remove lazy loading from thumbnail

[tvdeyen]

What is this pull request for?

Setting image.loading = "lazy" after image.src starts the fetch was a
no-op. The loading attribute is consulted before fetch begins, and for
detached Image instances the fetch starts immediately when src is set.
The attribute never actually deferred anything here. Removing it makes
the code honest about what happens and prevents accidental activation
if the order is ever reversed in a context where lazy would be harmful,
such as the crop dialog.

And scope the thumbnail image CSS to direct children

The [loading] opacity rule used a descendant selector which also matched
the cloned img that CropperJS moves into its own canvas inside the
thumbnail. If the clone's load event fired before the original's, the
cropper UI was built while the loading attribute was still set, leaving
the image inside the cropper invisible until the original fired its own
load event. Scoping the rule to direct children keeps the hide/reveal
behavior for our own placeholder while leaving nested imgs untouched.

Checklist

• I have followed Pull Request guidelines
• I have added a detailed description into each commit message
• I have added tests to cover this change

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.06%. Comparing base (96cdfd4) to head (c8054ff).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3845   +/-   ##
=======================================
  Coverage   98.06%   98.06%           
=======================================
  Files         322      322           
  Lines        8530     8530           
=======================================
  Hits         8365     8365           
  Misses        165      165           

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[alchemycms-bot]

💔 Some backports could not be created

Status	Branch	Result
❌	8.1-stable	Backport failed because of merge conflicts You might need to backport the following PRs to 8.1-stable: - fix(alchemy-notice): Use default font size for headings
✅	8.2-stable

Manual backport

To create the backport manually run:

backport --pr 3845

Questions ?

Please refer to the Backport tool documentation and see the Github Action logs for details

[alchemycms-ci-bot]

💚 All backports created successfully

Status	Branch	Result
✅	8.1-stable

Questions ?

Please refer to the Backport tool documentation