Improve predicate test coverage and stabilize CoreData tests

[colemancda]

Follow-up to #35.

Coverage

The coverage bot flagged a 1% overall drop, so the uncovered paths in the new predicate code were reviewed line by line:

• Removed an unused PredicateValue.aggregateValues accessor — dead code from the traversal work, which the coverage report surfaced.
• Added conversion tests for the paths that had no coverage: <= and > comparisons, contains over a collection property, localizedStandardContains, and an @objc root whose key paths resolve through Key-Value Coding (the path real CoreData usage takes, previously untested since the fixtures are plain structs).
• Added evaluator tests for null relationships, an ALL/ANY modifier applied to a plain attribute, and a key path whose leading key isn't a relationship.

Line coverage: FoundationPredicate.swift 90.8% → 96.3%, Evaluate.swift 95.9% → 97.5%, with every function in the conversion layer now executed.

Test stabilization

While running the suite repeatedly, CoreDataModelTests.modifierPredicateFetch was found to fail intermittently (about 2 failures in 9 full-suite runs), with crashes such as NSArray element failed to match the Swift Array Element type. It passes 10/10 in isolation, so the trigger is parallel execution: four suites each build their own NSPersistentStoreCoordinator/NSManagedObjectModel and ran concurrently.

Those four suites are now @Suite(.serialized). No failure appeared in 12 consecutive runs afterwards, though one failure did occur across 7 later coverage-instrumented runs — so this reduces the flakiness rather than provably eliminating it, since .serialized only orders tests within a suite and the suites still run in parallel with each other. This is the same family of intermittent macOS crash CI has been reporting on recent PRs, and it is reproducible locally, so it is not a CI runner problem. Fully removing cross-suite CoreData parallelism would be the next step if it recurs.

[github-code-quality]

Code Coverage Overview

Languages: Swift

Swift / code-coverage/llvm-cov

The overall coverage in commit c34b014 in the feature/predicate branch is 95%. The coverage in commit 65503f5 in the master branch is 94%.

Show a code coverage summary of the most impacted files.

File	master 65503f5	feature/predicate c34b014	+/-
Sources/CoreMod.../Evaluate.swift	95%	97%	+2%
Sources/CoreMod...Predicate.swift	89%	94%	+5%