Optimize memory usage for large vocabularies by replacing loadTree() with count queries in TaxonomyManagerTree and TaxonomyManagerHelper

Here we have issue with PHPStan that is not related to the Merge Request, so I think it can be reviewed.

thanks, approach makes sense to me. Just one confusion about range().

The issue PR was updated.

Thanks!

The tests fails look unrelated to me and should be cleaned up in a separate issue.

Cleaned up test fails in 🐛 Method Drupal\term_merge\Form\MergeTerms::__construct() invoked with 2 parameters, 3 required. Active .

Merged, thanks!