Check whether progress reporting could be incorrect in certain cases (technical debt)

Background

!1482 (merged) adds a way to report progress when loading elements, but there are points where an element might be loaded or resolved that happen outside the scope of a SimpleTask.

Tests have been added to check that the tallies are correct when loading across a junction in a simple case, but the full spread of possibilities where elements might be loaded or resolved has not been investigated.

Task description

• Trace through loader code to see which points Loader._collect_element are called to see which ones will and won't have a Task passed in.
• Assess whether a Task should be passed in for those cases.
• Write tests to cover any edge cases that are not already covered

Acceptance Criteria

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