Use PyQt6 item data roles in log viewer

[trissim]

What changed

• replace the two remaining legacy Qt.DisplayRole accesses in the log viewer with Qt.ItemDataRole.DisplayRole
• exercise both search precomputation and delegate sizing under PyQt6

This is the declaration-owner fix for OpenHCS issue #61; no OpenHCS-side compatibility shim is introduced.

Verification

PYTHONPATH=src:../ObjectState/src:../python-introspect/src QT_QPA_PLATFORM=offscreen ../../.venv/bin/python -m pytest tests/test_log_viewer_lifecycle.py -q
5 passed

[augmentcode]

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[Copilot]

Pull request overview

This PR completes the PyQt6 migration in the log viewer by replacing the remaining legacy Qt.DisplayRole usages with the scoped Qt.ItemDataRole.DisplayRole, and adds a regression test to exercise both search-match precomputation and delegate sizing under PyQt6.

Changes:

• Updated LogItemDelegate to use Qt.ItemDataRole.DisplayRole when reading model text for search precomputation.
• Updated LogItemDelegate.sizeHint() to use Qt.ItemDataRole.DisplayRole when sizing rows.
• Added a PyQt6-focused lifecycle test that executes _precompute_search_matches() and sizeHint() and asserts expected behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
tests/test_log_viewer_lifecycle.py	Adds a regression test to exercise delegate search precomputation + sizing with PyQt6-scoped item data roles.
src/pyqt_reactive/widgets/log_viewer.py	Replaces the remaining Qt.DisplayRole accesses with Qt.ItemDataRole.DisplayRole in the log viewer delegate logic.

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