PERF: Avoid copy in pystac for ItemCollections

[TomAugspurger]

Related Issue(s): #

#49
stac-utils/pystac#454

Description:

This uses the preserve_dict keyword added in stac-utils/pystac#454 to avoid a deepcopy on the items passed to pystac.ItemCollection. In these cases, we have the only reference to dictionary so it should be safe to mutate. As a small test:

import pystac_client

datetime = "2019-12-13/2019-12-13"
catalog = pystac_client.Client.open("https://planetarycomputer.microsoft.com/api/stac/v1")
%time search = catalog.search(collections=["sentinel-2-l2a"], datetime=datetime, limit=500)

That took ~20s on the latest released version and 14s after applying this change.

PR Checklist:

• Code is formatted
• Tests pass
• Changes are added to the CHANGELOG

[codecov-commenter]

Codecov Report

Merging #90 (2039c9c) into main (cae8956) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #90   +/-   ##
=======================================
  Coverage   77.46%   77.46%           
=======================================
  Files           9        9           
  Lines         537      537           
=======================================
  Hits          416      416           
  Misses        121      121           

Impacted Files	Coverage Δ
pystac_client/item_search.py	77.82% <100.00%> (ø)

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[TomAugspurger]

cc @gadomski