Add operators: RegexSplit, TokensSplit, Chunk

[elronbandel]

Usage examples:

Chunk(field="x", size=2)
RegexSplit(field="text", by=r"([\s,!?]+)")
TokensSplit(field="text", model="bert-base-uncased")

All the examples above has input-output examples in the tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.18%. Comparing base (422212f) to head (95e7258).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #749      +/-   ##
==========================================
+ Coverage   91.15%   91.18%   +0.02%     
==========================================
  Files          98       98              
  Lines        9968    10001      +33     
==========================================
+ Hits         9086     9119      +33     
  Misses        882      882              

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