refactor: break out default batch file writer into separate class

[kgpayne]

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📚 Documentation preview 📚: https://meltano-sdk--1668.org.readthedocs.build/en/1668/

[codecov]

Codecov Report

Merging #1668 (37d1262) into main (2974649) will increase coverage by 0.01%.
The diff coverage is 95.12%.

@@            Coverage Diff             @@
##             main    #1668      +/-   ##
==========================================
+ Coverage   85.05%   85.07%   +0.01%     
==========================================
  Files          58       59       +1     
  Lines        4845     4864      +19     
  Branches      805      807       +2     
==========================================
+ Hits         4121     4138      +17     
- Misses        526      527       +1     
- Partials      198      199       +1     

Impacted Files	Coverage Δ
singer_sdk/helpers/_batch.py	88.78% <60.00%> (-1.42%)	⬇️
singer_sdk/batch.py	100.00% <100.00%> (ø)
singer_sdk/streams/core.py	83.01% <100.00%> (-0.66%)	⬇️

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[kgpayne]

@edgarrmondragon this is to better reuse batch file writers on the target side. I.e. cases where the target supports batch files (in json or csv) but receives records. E.g. target-snowflake

[edgarrmondragon]

@edgarrmondragon this is to better reuse batch file writers on the target side. I.e. cases where the target supports batch files (in json or csv) but receives records. E.g. target-snowflake

@kgpayne This is looking great. Should we document these new batcher classes in the reference section (which is actually getting crowded imo)?