Lazy-load process-to-human-readable-title mapping in status tree

The simplified status tree uses a `TITLE_MAPPING` to render human-readable titles of registered workflows and calculations. The mapping is extended dynamically by registering titles from plugin processes. However, at the moment, the extension is done at load time. Consider deferring it to time of use + caching for efficiency. See comment here - https://github.com/aiidalab/aiidalab-qe/pull/1512/changes#r3757646638.

Start with the simplified status tree and its TITLE_MAPPING, then inspect where plugin processes register human-readable titles and review the linked pull request comment. Defer extending the mapping until a title is requested and cache the result so repeated lookups avoid the registration work; existing status-tree behavior should remain unchanged.

Rédigé par le modèle d'indexation à partir du texte de l'issue.