test: verify ArrayBuffer ownership across native roundtrips

[mrousavy]

The existing ArrayBuffer copy and bounce tests could pass when ownership was wrong because they checked only a byte copied before the roundtrip. Replace them with shared-memory and copy-isolation checks using the existing parameterized C++ and Swift/Kotlin Harness suite.

Cover JS buffers, native allocations, and native-backed buffers. Repeated bounces must share writes through the original and returned aliases; copies must preserve length and distinctive bytes while remaining independent after JS and native mutations. Reuse the existing native readers/writers and retain the JS identity test.

Validation:

• Local iOS Debug build succeeded with Xcode 26.6.
• Focused iOS Harness run: 14 passed (12 ownership cases plus 2 identity cases), on iPhone 17 Pro / iOS 26.5 using C++ and Swift.
• Package build, example TypeScript check, targeted ESLint, and diff check passed.
• Temporary assertion mutation check rejects aliased copies, copied bounces, and native writes to detached storage.
• Android runtime validation was not run locally. CI is intentionally cancelled after PR creation to conserve Actions minutes.

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1 Skipped Deployment

Project	Deployment	Actions	Updated
nitro-docs	Skipped		Sep 5, 2026 3:38pm UTC