Use cbor2pure by default

[cffls]

This commit will ensure pure python version of cbor2 is used when installing pycardano for the first time, without modifying any dependencies. Users are still free to use cbor2 if speed is preferred over correctness by setting CBOR_C_EXETENSION=1 in their environment.

A dynamic cbor2 module is also exported by pycardano, which allows users to use if they want to write custom version of decoder without worrying about using the wrong cbor library with pycardano.

from pycardano.cbor2 import cbor2

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.57%. Comparing base (40e18d5) to head (d1c151d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pycardano/cbor.py	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #475      +/-   ##
==========================================
- Coverage   90.64%   90.57%   -0.08%     
==========================================
  Files          33       34       +1     
  Lines        5153     5157       +4     
  Branches      781      782       +1     
==========================================
  Hits         4671     4671              
- Misses        304      306       +2     
- Partials      178      180       +2     

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[nielstron]

Thanks for finally tackling this! Overall the approach is sound, just 2 minor notes.

[cffls]

Thanks for reviewing and the suggestions! All tests are passing, merging now.

[theeldermillenial]

@cffls This is huge! Thanks. It will make things much easier.