fix: prevent null WrappedElement during concurrent component re-renders

[Nacl-HCl]

Pull request description

Fixes a race condition in WrapperBase<TElement>.WrappedElement where an element returned by Find() could return null and throw a NullReferenceException on member access when the component re-renders on another thread at the same time (e.g. from a background timer or asynchronous event).

Cause

The getter previously read the element field twice:
`csharp
if (element is null)
element = elementFactory.GetElement();

return element;
WhenOnElementReplacedresetelementtonullbetween the check and the return statement, the getter returnednull`.

Fix

Changed the getter to evaluate via null-coalescing assignment element ??= elementFactory.GetElement<TElement>(), which ensures the reference is evaluated once and never returns null. Also updated the verified generator snapshot and added a concurrent regression test.

Closes #1937

PR meta checklist

• Pull request is targeted at main branch for code
• Pull request is linked to all related issues, if any.
• I have read the CONTRIBUTING.md document.

Code PR specific checklist

• My code follows the code style of this project and AspNetCore coding guidelines.
• My change requires a change to the documentation.
• I have updated the appropriate sub section in the CHANGELOG.md.
• I have added, updated or removed tests to according to my changes.
  • All tests passed.

[linkdotnet]

Looking good - let's wait what CI/CD is saying and then get that in.
Thanks for that

[linkdotnet]

Using < and > leads to issues (see other generic usages) as we "merge" that inside the csproj - so it leads to malformed csproj file. Either drop the < > or use < stuff