Extract the repeated line-position calculation pattern into a
_calculate_line_positions() helper. The same 4-line pattern was
duplicated across _strategy_trimmed_boundary, _strategy_block_anchor,
_strategy_context_aware, and _find_normalized_matches. Also
standardizes the end_pos clamping (some sites used min(), some used
an if-guard).
Based on PR #1604 by aydnOktay.
Co-authored-by: aydnOktay <aydnOktay@users.noreply.github.com>