Problems view title update blocks UI 2-36s: Markers.getMarkerCounts walks all markers, each doing ElementTree lookups #4404

With a large workspace (tens of thousands of markers), any marker change
triggers ExtendedMarkersView.updateTitle -> Markers.getMarkerCounts, which
iterates ALL markers; each Marker.getAttribute() performs a workspace
ElementTree traversal. Durations escalated over 2 days: 2.4s -> 17s (BLOCKED on
marker lock) -> 36s.

Samples:
Markers.getMarkerCounts -> Marker.getAttribute -> MarkerManager.findMarkerInfo
-> Workspace.getResourceInfo -> ElementTree.getElementData

Also: editor caret movement triggers ExtendedMarkersView.setSelection ->
Markers.getMarkerItem (BLOCKED 17s) waiting on the same marker model lock.

Expected: incremental counts or caching; selection lookup should not contend
with bulk counting.

(search "Problems view slow" / "getMarkerCounts" first and add samples if an
open issue exists)