Render DNF and DNS instead of raw negative result sentinels

[coder13]

Problem

Competition result values use WCA sentinel values for non-results:

• -1 means DNF
• -2 means DNS

The current result formatter passes these values through numeric event formatting, so result tables can display the raw values -1 and -2. This is visible in the Lipnica Wielka Open 2026 results screenshot.

Expected behavior

Every displayed attempt, best, average, or mean result should render the WCA status text instead of the sentinel number:

• -1 -> DNF
• -2 -> DNS

Acceptance criteria

• Negative WCA result sentinels are handled before event-specific formatting.
• -1 renders as DNF.
• -2 renders as DNS.
• Normal centisecond, FMC, and Multi-Blind result formatting remains unchanged.
• Existing zero-value placeholder behavior remains unchanged.
• Add focused regression tests for both sentinels.