Add support for Foundation.SortDescriptor

[colemancda]

Resolves #14

Rounds out Foundation.SortDescriptor support with full bidirectional conversions, plus cross-platform SortComparator/SortOrder support via swift-foundation's FoundationEssentials:

• FetchRequest.SortDescriptor conforms to SortComparator (comparing ModelData), with an order: SortOrder property and order-based initializers — available on all platforms with Foundation, not just Darwin.
• FetchRequest.SortDescriptor.toFoundation(comparing:) converts back to Foundation.SortDescriptor, returning nil for function-based sort terms, which have no Foundation equivalent.
• NSSortDescriptor round-trip: init?(_:) (nil when the sort descriptor has no key path) and toFoundation().
• New FetchRequest convenience initializer accepting [Foundation.SortDescriptor<Root>].
• CoreDataModel fetch request bridging now reuses the shared toFoundation() conversion.
• Tests covering round-trips, sort orders, SortComparator sorting, the nil cases, and the new initializers.

[github-code-quality]

Code Coverage Overview

Languages: Swift

Swift / code-coverage/llvm-cov

The overall coverage in commit 635e2a0 in the feature/predicate branch remains at 95%, unchanged from commit 556dca9 in the master branch.

Show a code coverage summary of the most impacted files.

File	master 556dca9	feature/predicate 635e2a0	+/-
Sources/CoreDat...chRequest.swift	100%	100%	0%
Sources/CoreMod...chRequest.swift	100%	100%	0%
Sources/CoreMod...escriptor.swift	100%	100%	0%
Sources/CoreModel/Locked.swift	0%	70%	+70%

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_{Updated August 16, 2026 14:06 UTC}