When instantiating ItemCollections clone items by default

[jsignell]

Related Issue(s):

• closes ItemCollection constructor should clone items in iterator by default #859

Description:

NOTE this PR changes the behavior when adding item collections. After this PR adding item collections will no longer dedupe items.

PR Checklist:

• Code is formatted (run pre-commit run --all-files)
• Tests pass (run scripts/test)
• Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01 ⚠️

Comparison is base (7b704a5) 90.32% compared to head (164876f) 90.32%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1016      +/-   ##
==========================================
- Coverage   90.32%   90.32%   -0.01%     
==========================================
  Files          47       47              
  Lines        6184     6181       -3     
  Branches      929      927       -2     
==========================================
- Hits         5586     5583       -3     
  Misses        420      420              
  Partials      178      178              

Impacted Files	Coverage Δ
pystac/item_collection.py	91.54% <100.00%> (-0.35%)	⬇️

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[gadomski]

Needs a CHANGELOG entry.