add tests as part of package + platform

[mshehan]

Swift 6.0 Upgrade and Iterative Model Loading

This PR updates the library to Swift 6.0 and improves the model loading process with several key enhancements:

• Upgrades Swift version from 4.0 to 6.0
• Updates Package.swift to support iOS 12+, macOS 10.14+, and tvOS 12+
• Adds proper resource handling for test fixtures
• Implements conditional UIKit imports to improve cross-platform compatibility
• Adds an iterative approach to loadIncluded to prevent stack overflows with deeply nested relationships
• Makes JSONAPIFactory and JSONAPIStore conform to the Collection protocol
• Adds comprehensive tests for the new iterative loading approach
• Improves error handling with assertion failures when model creation fails

The iterative loading approach replaces the recursive implementation to prevent potential stack overflows when dealing with complex nested relationships, while maintaining the same functionality.

[mshehan]

• add tests as part of package + platform #4 👈 (View in Graphite)
• Swift Package Manager #3
• master

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[mshehan]

Merge activity

• Jul 11, 5:01 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• Jul 11, 5:02 AM UTC: Graphite rebased this pull request as part of a merge.
• Jul 11, 5:04 AM UTC: @mshehan merged this pull request with Graphite.