allow sorting results table by solve attempt columns

[Victus0660]

Motivation

Currently, WCA Live displays round results strictly by official ranking. However, in events like FMC (3x3x3 Fewest Moves), competitors who DNF their overall mean often have impressive single attempts that get buried in the list. Allowing users to sort by individual solve attempt columns makes it easy to see the best scores for each attempt and analyze performance per solve.

Summary of Changes

• Client-side sorting logic: Added sortResultsByColumn() in client/src/lib/result.js to sort by attempt index or stat column while properly prioritizing valid attempts over incomplete (DNF/DNS/skipped) entries.
• Header interaction: Integrated Material UI <TableSortLabel> into attempt headers (1, 2, 3, etc.) and stat headers (Best, Average/Mean) in RoundResultsTable.jsx.
• State management: Added sort state in RoundResults.jsx with a 3-step click cycle (Ascending -> Descending -> Reset to official server order).
• Preserved official ranking: Kept official ranking numbers in the # column so users can easily reference official placements while sorting.
• Unit tests: Added test suite covering sortResultsByColumn() in client/src/lib/tests/result.test.js.

Verification

• Tested with FMC and standard timed events.
• Confirmed valid solves sort properly while DNFs stay at the bottom in both ascending and descending modes.
• Verified clearing sort resets the view back to default server rankings.