Allow Q: ?Sized in Itertools::contains

[Alexendoo]

To enable .contains("foo") on an Iterator<Item = String> and similar

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.32%. Comparing base (6814180) to head (ccd68d2).
Report is 111 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #971      +/-   ##
==========================================
- Coverage   94.38%   94.32%   -0.07%     
==========================================
  Files          48       49       +1     
  Lines        6665     6708      +43     
==========================================
+ Hits         6291     6327      +36     
- Misses        374      381       +7     

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[phimuemue]

Thanks.