CRC tools for computation and research

[phil777]

Checklist:

• If you are new to Scapy: I have checked CONTRIBUTING.md (esp. section submitting-pull-requests)
• I squashed commits belonging together
• I added unit tests or explained why they are not relevant
• I executed the regression tests (using tox)
• If the PR is still not finished, please create a Draft Pull Request

This PR provides a CRC toolbox to compute CRC, create new ones, or search for possible CRC present in a byte string.

[codecov]

Codecov Report

❌ Patch coverage is 46.81648% with 142 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.78%. Comparing base (12a3752) to head (f890e16).

Files with missing lines	Patch %	Lines
scapy/crc.py	46.61%	142 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4855      +/-   ##
==========================================
- Coverage   80.88%   80.78%   -0.11%     
==========================================
  Files         368      369       +1     
  Lines       90340    90607     +267     
==========================================
+ Hits        73069    73194     +125     
- Misses      17271    17413     +142     

Files with missing lines	Coverage Δ
scapy/all.py	100.00% <100.00%> (ø)
scapy/crc.py	46.61% <46.61%> (ø)

... and 6 files with indirect coverage changes

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