Add JS/Swift Date support

[bsneed]

• Added conversion for JS date to swift Date.
• Added round trip tests

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.48%. Comparing base (293df9d) to head (5d07b34).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
Sources/Substrata/Internals/Conversion.swift	89.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #10      +/-   ##
==========================================
- Coverage   79.98%   79.48%   -0.51%     
==========================================
  Files          12       12              
  Lines        1604     1194     -410     
==========================================
- Hits         1283      949     -334     
+ Misses        321      245      -76     

Files with missing lines	Coverage Δ
Sources/Substrata/Utilities/Extensions.swift	54.70% <100.00%> (-0.52%)	⬇️
Sources/Substrata/Internals/Conversion.swift	73.34% <89.47%> (+0.77%)	⬆️

... and 10 files with indirect coverage changes

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