fix where deepCopy was not actually deep coping elements.

[skhugh]

What this PR does / why we need it?

fix where deepCopy was not actually deep coping elements.

Any background context you want to provide?

What are the relevant tickets?

Fixes #

Checklist

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Merging #71 (4a4c7e2) into main (9562b3d) will decrease coverage by 0.24%.
The diff coverage is 61.11%.

@@            Coverage Diff             @@
##             main      #71      +/-   ##
==========================================
- Coverage   81.09%   80.84%   -0.25%     
==========================================
  Files          52       52              
  Lines        2348     2355       +7     
  Branches      336      336              
==========================================
  Hits         1904     1904              
- Misses        255      260       +5     
- Partials      189      191       +2     

Impacted Files	Coverage Δ
...in/kotlin/dev/yorkie/document/crdt/RgaTreeSplit.kt	64.86% <45.45%> (-1.02%)	⬇️
...c/main/kotlin/dev/yorkie/document/crdt/TextInfo.kt	93.10% <80.00%> (-3.06%)	⬇️
...main/kotlin/dev/yorkie/document/crdt/CrdtObject.kt	90.69% <100.00%> (ø)
...c/main/kotlin/dev/yorkie/document/crdt/CrdtText.kt	87.14% <100.00%> (ø)
...ain/kotlin/dev/yorkie/document/crdt/CrdtElement.kt	78.94% <0.00%> (-5.27%)	⬇️
...c/main/kotlin/dev/yorkie/document/crdt/RhtPQMap.kt	79.71% <0.00%> (-1.45%)	⬇️

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[hackerwins]

Thanks for your contribution.