fix: encode pointer object properties properly when batching

[cbaker6]

New Pull Request Checklist

• [x] I am not disclosing a vulnerability.
• [x] I am creating this PR in reference to an issue.

Issue Description

Batch saving objects that has other parse objects as properties are not encoded correctly, causing the server to throw errors.

Related issue: #387

Approach

Ensure properties that are already savedParseObject's are converted to Parse pointers during encoding.

TODOs before merging

• [x] Add tests

[parse-github-assistant[bot]]

Thanks for opening this pull request!

• 🎉 We are excited about your hands-on contribution!

[codecov[bot]]

Codecov Report

Merging #390 (ae48ead) into main (50f655b) will increase coverage by 0.03%. The diff coverage is 97.22%.

@@            Coverage Diff             @@
##             main     #390      +/-   ##
==========================================
+ Coverage   89.15%   89.19%   +0.03%     
==========================================
  Files         156      156              
  Lines       14528    14553      +25     
==========================================
+ Hits        12953    12981      +28     
+ Misses       1575     1572       -3     

Impacted Files	Coverage Δ
Sources/ParseSwift/API/BatchUtils.swift	100.00% <ø> (ø)
Sources/ParseSwift/Objects/ParseObject.swift	87.29% <96.96%> (+2.03%)	:arrow_up:
Sources/ParseSwift/Objects/ParseUser.swift	85.80% <96.96%> (-0.50%)	:arrow_down:
Sources/ParseSwift/Objects/ParseInstallation.swift	84.90% <97.22%> (-0.56%)	:arrow_down:
Sources/ParseSwift/API/API+Command.swift	89.21% <100.00%> (ø)
...urces/ParseSwift/API/API+NonParseBodyCommand.swift	81.59% <100.00%> (+0.49%)	:arrow_up:
Sources/ParseSwift/Coding/ParseEncoder.swift	78.03% <100.00%> (-0.21%)	:arrow_down:
Sources/ParseSwift/LiveQuery/ParseLiveQuery.swift	76.75% <0.00%> (+0.58%)	:arrow_up:
... and 1 more

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