Deepcopy Asset.extra_fields when cloning

[duckontheweb]

Related Issue(s):

• Closes Asset: clone() doesn't clone extra_fields #820

Description:

Uses deepcopy on Asset.extra_fields when cloning so that mutating the cloned Asset's extra fields does not mutate the original asset.

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.

[m-mohr]

Thank you @duckontheweb I'd also be fine with a shallow copy of Asset.extra_fields because that is what the documentation says, but also fine with a deep copy if documented properly.

[duckontheweb]

Thank you @duckontheweb I'd also be fine with a shallow copy of Asset.extra_fields because that is what the documentation says, but also fine with a deep copy if documented properly.

@m-mohr Which documentation are you referring to here? The Asset.clone docs just say "Clones this asset.", which seems vague enough to cover both cases. I'll update that to be more specific, but is there another place where it specifically suggests we're doing a shallow copy?

[m-mohr]

Oh yeah, sorry, I was confusing this with the description of clone for Items/Collections...

[duckontheweb]

I updated the Asset.clone docs and added a regression test to be sure Asset.roles is also not mutated on clones.

[codecov-commenter]

Codecov Report

Merging #826 (696ded3) into main (0f308cd) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #826      +/-   ##
==========================================
+ Coverage   94.33%   94.34%   +0.01%     
==========================================
  Files          83       83              
  Lines       11898    11923      +25     
  Branches     1389     1390       +1     
==========================================
+ Hits        11224    11249      +25     
  Misses        495      495              
  Partials      179      179              

Impacted Files	Coverage Δ
pystac/asset.py	86.11% <100.00%> (ø)
tests/test_item.py	100.00% <100.00%> (ø)

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