MTN deterministic co_filename for dynamic code pickling

[tomMoral]

Set the co_filename to <dynamic-code> when pickling the code object to make the payload independent of where the code was defined.

TODO:

• add test
• add changelog

Fix #538

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.23%. Comparing base (f90f78a) to head (553025c).

❗ There is a different number of reports uploaded between BASE (f90f78a) and HEAD (553025c). Click for more details.

HEAD has 9 uploads less than BASE

Flag	BASE (f90f78a)	HEAD (553025c)
	20	11

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #560      +/-   ##
==========================================
- Coverage   96.34%   89.23%   -7.12%     
==========================================
  Files           3        3              
  Lines         575      576       +1     
  Branches      121      121              
==========================================
- Hits          554      514      -40     
- Misses         11       49      +38     
- Partials       10       13       +3     

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[ogrisel]

No idea on how to debug the random failure but I found a typo...

[tomMoral]

The failure is deterministic and only happening on windows and on this branch (see #562 running from master and working).
Not sure how to debug either...