RWS: render negative times correctly

[prandla]

currently, if there's any submissions that were made before the start of the contest, RWS renders them.. suboptimally:

the time formatting is from TimeView.js, and the way it's used there is actually safe for negative times, but the way it's used in UserDetails.js is not. I moved the negative handling into the format_time function itself, so that UserDetails can also correctly render them.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.70%. Comparing base (513ee4b) to head (a11121d).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1637      +/-   ##
==========================================
+ Coverage   54.68%   54.70%   +0.01%     
==========================================
  Files         335      335              
  Lines       27354    27354              
==========================================
+ Hits        14958    14963       +5     
+ Misses      12396    12391       -5     

Flag	Coverage Δ
functionaltests	0.00% <ø> (ø)
unittests	54.70% <ø> (+0.01%)	⬆️

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