feat: add MonoChild

[moul]

No description provided.

[github-actions]

Expected release notes (by @moul)

features:
add MonoChild (485219a)

• I hereby acknowledge these release notes are 🥙 AWESOME 🥙

[codecov]

Codecov Report

Merging #5 into master will decrease coverage by 7.40%.
The diff coverage is 77.77%.

@@             Coverage Diff             @@
##            master       #5      +/-   ##
===========================================
- Coverage   100.00%   92.59%   -7.41%     
===========================================
  Files            4        5       +1     
  Lines           18       27       +9     
===========================================
+ Hits            18       25       +7     
- Misses           0        1       +1     
- Partials         0        1       +1     

Flag	Coverage Δ
#unittests	92.59% <77.77%> (-7.41%)	⬇️

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Impacted Files	Coverage Δ
concurrency.go	77.77% <77.77%> (ø)

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[github-actions]

🎉 This PR is included in version 1.4.0 🎉

The release is available on GitHub release

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