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.