Introduce timed flush

[zix99]

Timed flush allows streams (stdin, following) to flush a batch before an entire batch has read if a duration times out. Defaults to 250ms

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[codecov-commenter]

Codecov Report

Merging #69 (da2aa88) into master (6ab0795) will increase coverage by 0.01%.
The diff coverage is 82.75%.

@@            Coverage Diff             @@
##           master      #69      +/-   ##
==========================================
+ Coverage   82.99%   83.01%   +0.01%     
==========================================
  Files          80       80              
  Lines        2964     2991      +27     
==========================================
+ Hits         2460     2483      +23     
- Misses        362      365       +3     
- Partials      142      143       +1     

Impacted Files	Coverage Δ
pkg/extractor/batchers/readerBatcher.go	0.00% <0.00%> (ø)
pkg/extractor/batchers/batcher.go	83.48% <85.18%> (+0.55%)	⬆️
pkg/extractor/batchers/tailBatcher.go	52.38% <100.00%> (ø)

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