Fix failed pkg_resources imports

[techalchemy]

Fix parsing of non-utf8 encoded setup.py files

• Add encoding detection fallback for ast paring of setup.py
• Fixes AST parsing fails on non-utf8 setup.py files #205

[ghost]

DeepCode's analysis on #27257f found:

• ❌ 0 critical issues. ⚠️ 1 warning and 0 minor issues. ✔️ 1 issue were fixed.

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[codecov]

Codecov Report

Merging #211 into master will decrease coverage by 0.1%.
The diff coverage is 60%.

@@            Coverage Diff             @@
##           master     #211      +/-   ##
==========================================
- Coverage   63.36%   63.25%   -0.11%     
==========================================
  Files          13       13              
  Lines        5546     5549       +3     
  Branches     1345     1345              
==========================================
- Hits         3514     3510       -4     
- Misses       1583     1589       +6     
- Partials      449      450       +1

Impacted Files	Coverage Δ
src/requirementslib/models/setup_info.py	67.31% <60%> (-0.1%)	⬇️
src/requirementslib/models/cache.py	41.57% <0%> (-3.94%)	⬇️
src/requirementslib/models/dependencies.py	57.84% <0%> (+0.65%)	⬆️

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