Stop shadowing Task._stop and Task._lastException (CodeQL java/field-masks-super-field)

[vharseko]

Summary

Addresses the java/field-masks-super-field alerts in StreamLoader and
StreamSaver. Both classes extend Task and redeclared _stop and
_lastException, which Task already declares, so the subclasses shadowed the
base fields instead of sharing them — a real defect, not just style.

File	Field	Superclass field	Effect of the shadow
StreamSaver.java	_stop (boolean)	Task._stop (AtomicBoolean)	save loops never saw a cancellation request
StreamSaver.java	_lastException	Task._lastException	recorded failure never reached the task status
StreamLoader.java	_stop, _lastException	Task._stop, Task._lastException	dead shadow fields, never read or written

Details

• StreamSaver._stop — Task._stop is an AtomicBoolean that Task.stop()
  flips to request cancellation. StreamSaver's own boolean _stop was never
  assigned, so saveAll, saveTrees and the traversal loop kept running even
  after a stop was requested. The shadow is removed and the loops now test the
  inherited _stop.get().
• StreamSaver._lastException — Task reports _lastException in the task
  status; StreamSaver wrote its own copy, so the status stayed none. Removing
  the shadow lets the recorded exception surface.
• StreamLoader — its _stop / _lastException were never read or written,
  so they are just removed.

For a normal (non-cancelled) run _stop is false throughout, so the loops
behave exactly as before; the change only lets a cancellation take effect and the
recorded exception appear in the task status.

Not changed here

The two remaining alerts on InstallExternalDependencyMojo.installer and
AbstractExternalDependencyMojo.artifactFactory are intentional: these are
Maven 2 @component fields re-declared in the plugin's own source so the
QDox-based plugin-descriptor generator emits the Plexus injection requirement
(the base classes live in compiled Maven artifacts whose @component tags the
generator cannot see). Removing them would drop the injection and NPE at runtime,
so they are left as-is.

Testing

mvn -o -pl persistit/core compile — BUILD SUCCESS.