fix: Expose isSaved method on ParseFile and ParseOperation

[cbaker6]

New Pull Request Checklist

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

Issue Description

Approach

TODOs before merging

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

[codecov]

Codecov Report

Merging #135 (4f49f11) into main (5817123) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #135      +/-   ##
==========================================
- Coverage   91.34%   91.33%   -0.01%     
==========================================
  Files         175      175              
  Lines       15466    15472       +6     
==========================================
+ Hits        14128    14132       +4     
- Misses       1338     1340       +2     

Files Changed	Coverage Δ
Sources/ParseSwift/Protocols/Savable.swift	0.00% <ø> (ø)
Sources/ParseSwift/Types/ParseFile.swift	94.71% <100.00%> (+0.07%)	⬆️
Sources/ParseSwift/Types/ParseOperation.swift	99.52% <100.00%> (+<0.01%)	⬆️

... and 1 file with indirect coverage changes