fix: introduce asyncio.Lock

[iomz]

Protect the access to the shared buffer for on_aggregated_data
cf. https://docs.python.org/3/library/asyncio-sync.html#lock

[codecov]

Codecov Report

Merging #24 (629f684) into main (87decf8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #24   +/-   ##
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  Coverage   85.63%   85.63%           
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  Files           7        7           
  Lines         376      376           
  Branches       16       16           
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  Hits          322      322           
  Misses         50       50           
  Partials        4        4