feat: assert each item in a collection or iterator

[haraldmaida]

Provide the possibility to assert each element of a collection or iterator.

Added the method Spec::each_item() that enables users to write assertions that are executed for each item in a collection or iterator.

[codecov]

Codecov Report

Attention: Patch coverage is 93.18182% with 3 lines in your changes missing coverage. Please review.

Project coverage is 96.13%. Comparing base (dee70df) to head (b2dbe01).

Files with missing lines	Patch %	Lines
src/spec/mod.rs	93.02%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #35      +/-   ##
==========================================
+ Coverage   96.07%   96.13%   +0.05%     
==========================================
  Files          25       25              
  Lines        2806     2849      +43     
  Branches     2806     2849      +43     
==========================================
+ Hits         2696     2739      +43     
  Misses        106      106              
  Partials        4        4              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.