Refactor connections to allow early release back to connection pool

[alisaifee]

Description

Refactoring of the request response flow to allow releasing the connection back to the connection pool if so desired. The primary objective is to allow higher concurrency with blocking connection pools.

This has a few side effects:

• response parsing can be performed inline when the data_received callback is called
• the pipeline implementation can possibly be simplified
• connections can be released back to the pool very early when using the ignore_replies context manager
• the parser implementation can be completely decoupled from the connection

[codecov[bot]]

Codecov Report

Merging #80 (d511fc2) into master (d511fc2) will not change coverage. The diff coverage is n/a.

:exclamation: Current head d511fc2 differs from pull request most recent head c61f2c6. Consider uploading reports for the commit c61f2c6 to get more accurate results

@@           Coverage Diff           @@
##           master      #80   +/-   ##
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  Coverage   98.14%   98.14%           
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  Files          57       57           
  Lines        7227     7227           
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  Hits         7093     7093           
  Misses        134      134           

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