Update custom marshaler and unmarshaler to accept context

[pgeiem]

Following my proposal #699 this PR add support for custom marshaler/unmarshaler with context support.
Adding:

• CustomUnmarshalerContext decoder option
• CustomMarshalerContext encoder option
• RegisterCustomMarshalerContext global function
• RegisterCustomUnmarshalerContext global function

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 97.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 77.93%. Comparing base (6a6c998) to head (032eb44).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #745      +/-   ##
==========================================
+ Coverage   77.85%   77.93%   +0.08%     
==========================================
  Files          22       22              
  Lines        8064     8094      +30     
==========================================
+ Hits         6278     6308      +30     
  Misses       1370     1370              
  Partials      416      416              

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[goccy]

Thank you for your contribution !! LGTM 👍