Added Timer::exec_count field

[matyhtf]

No description provided.

[codecov]

Codecov Report

Merging #4402 (249a637) into master (9dbff4c) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4402      +/-   ##
==========================================
- Coverage   51.42%   51.40%   -0.02%     
==========================================
  Files          73       73              
  Lines       14691    14692       +1     
==========================================
- Hits         7555     7553       -2     
- Misses       7136     7139       +3     

Impacted Files	Coverage Δ
src/core/timer.cc	83.19% <100.00%> (+0.14%)	⬆️
src/os/async_thread.cc	69.29% <0.00%> (-0.88%)	⬇️
src/os/process_pool.cc	57.43% <0.00%> (-0.46%)	⬇️
src/server/port.cc	50.27% <0.00%> (+0.27%)	⬆️

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