Use 4 spaces instead of tabs

• Merge !19 (merged) first

requested review from @faverge

mentioned in merge request !13 (merged)

mentioned in merge request !8 (closed)

marked the checklist item Merge !19 (merged) first as completed

added 2 commits

• 7f751e0f - 1 commit from branch solverstack:main
• 13d8bf53 - Convert tabs to 4 spaces characters

Compare with previous version

approved this merge request

mentioned in commit 681387a0

merged