Use ZSTD_compressStream2 with endOp argument

[mkitti]

• Change compress! to use ZSTD_compressStream2 rather than ZSTD_compressStream
• Add tests for endOp

This provides us with more flexibility regarding the streaming API. In particular
providing an endOp of :end will include the decompressed in the frame header.

Currently, this does not connect the transcode machinery with this functionality.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 32.17%. Comparing base (4c799fe) to head (8b977fa).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #49      +/-   ##
==========================================
+ Coverage   30.98%   32.17%   +1.19%     
==========================================
  Files           5        5              
  Lines         510      519       +9     
==========================================
+ Hits          158      167       +9     
  Misses        352      352              

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[nhz2]

Looks good to me.