perf: Do not use reducer if there is no callback in SignalInstance.resume

[Czaki]

This is followup to #277

Remove the whole reducing operation if there is no callback.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ab5dfc5) 100.00% compared to head (9ec3f99) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #278   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           23        23           
  Lines         1926      1929    +3     
=========================================
+ Hits          1926      1929    +3     

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[codspeed-hq]

CodSpeed Performance Report

Merging #278 will not alter performance

_{Comparing Czaki:remove_reducer_call_on_no_slot (9ec3f99) with main (ab5dfc5)}

Summary

✅ 66 untouched benchmarks

[Czaki]

Should I add test for it? (some mocking of reducer)

[tlambert03]

works for me!

[tlambert03]

Should I add test for it? (some mocking of reducer)

normally i'd say don't bother, but since we've got 100% coverage here, might as well keep it :)

[tlambert03]

actually... it's fine. the logic is so simple, and it does get covered by tests already. will merge. thanks!