nfe: Fix nfe gen

[rvalyi]

single file generation using:
xsdata generate --include-header nfelib/nfe/schemas/v4_0/leiauteNFe_v4.00.xsd --package nfelib.nfe.bindings.v4_0
to work around #131 and other related issues.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.55%. Comparing base (bc13784) to head (aebf1c4).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #142      +/-   ##
==========================================
- Coverage   94.02%   89.55%   -4.48%     
==========================================
  Files          10       10              
  Lines         335      335              
  Branches       29       29              
==========================================
- Hits          315      300      -15     
- Misses         10       25      +15     
  Partials       10       10              

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