Stringify arguments and results only when logging is enabled

[isra17]

One of our profiling profile shows that 40% of computing time is spent in repr call from ARQ. At the moment, even without logging this get called, which can be expensive on large inputs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.49%. Comparing base (94cd878) to head (5fe243b).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #463      +/-   ##
==========================================
+ Coverage   96.27%   96.49%   +0.21%     
==========================================
  Files          11       11              
  Lines        1074     1083       +9     
  Branches      209      191      -18     
==========================================
+ Hits         1034     1045      +11     
  Misses         19       19              
+ Partials       21       19       -2     

Files	Coverage Δ
arq/utils.py	100.00% <100.00%> (ø)
arq/worker.py	97.37% <100.00%> (+0.20%)	⬆️

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[samuelcolvin]

LGTM, can you add a test.

[isra17]

LGTM, can you add a test.

Done