feat: Static encoders/decoder access

[cbaker6]

New Pull Request Checklist

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

Issue Description

Currently encoders and decoders can only be accessed via instances of ParseObject's.

Related issue: #N/A

Approach

Allow the encoders/decoder to be accessed statically, not requiring an instance. The instance versions are still available as there can be times where it's easier to access the instance version.

TODOs before merging

• Add tests
• Add entry to changelog
• Add changes to documentation (guides, repository pages, in-code descriptions)

[codecov]

Codecov Report

Merging #259 (51ea0ec) into main (aeb363f) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #259      +/-   ##
==========================================
- Coverage   76.81%   76.80%   -0.01%     
==========================================
  Files          98       98              
  Lines       10412    10421       +9     
==========================================
+ Hits         7998     8004       +6     
- Misses       2414     2417       +3     

Impacted Files	Coverage Δ
Sources/ParseSwift/Coding/Extensions.swift	100.00% <100.00%> (ø)
Sources/ParseSwift/Objects/ParseUser.swift	79.64% <0.00%> (-0.32%)	⬇️

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