fix: write buffer uses correct flush interval and batch size under heavy load

[bednar]

part of #68

• CHANGELOG.md updated
• Rebased/mergeable
• Tests pass
• Sign CLA (if not already signed)

[codecov-io]

Codecov Report

Merging #69 into master will increase coverage by 0.09%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #69      +/-   ##
==========================================
+ Coverage   15.93%   16.02%   +0.09%     
==========================================
  Files          47       47              
  Lines        4593     4623      +30     
  Branches      144      224      +80     
==========================================
+ Hits          732      741       +9     
- Misses       3861     3862       +1     
- Partials        0       20      +20     

Impacted Files	Coverage Δ
Client/WriteApi.cs	0.00% <0.00%> (ø)
Client.Core/Arguments.cs	16.00% <0.00%> (-8.00%)	⬇️
Client.Core.Test/AbstractMockServerTest.cs	96.42% <0.00%> (-3.58%)	⬇️
Client.Core/Flux/Internal/FluxResultMapper.cs	41.12% <0.00%> (-2.81%)	⬇️
Client.Core/Internal/LoggingHandler.cs	24.39% <0.00%> (-2.44%)	⬇️
Client.Core/Flux/Domain/FluxRecord.cs	81.81% <0.00%> (-2.28%)	⬇️
Client.Core/Flux/Internal/FluxCsvParser.cs	93.92% <0.00%> (-1.66%)	⬇️
Client.Core.Test/AbstractTest.cs	73.13% <0.00%> (-1.50%)	⬇️
Client.Legacy/FluxClient.cs	98.31% <0.00%> (-0.57%)	⬇️
Client.Core/Exceptions/InfluxException.cs	87.75% <0.00%> (ø)
... and 4 more

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