Improve reusable TestCase and Swift Testing integration

[kudit]

What changed

This PR modernizes Compatibility's reusable test infrastructure, debugging/threading helpers, and Xcode test integration.

• Added the Compatibility Testing Library and ModuleTestEntry so reusable TestCases appear as named parameterized Swift Testing cases in SwiftPM and Xcode.
• Unified reusable test execution through one lifecycle with explicit parallel/serialized behavior, source-aware failures, and reliable cleanup of mutable debug settings.
• Consolidated debug formatting/source context and kept debug logging callable without requiring main-actor isolation.
• Corrected main so the helper itself can be called from any thread while only its closure is main-actor isolated; full-runtime WebAssembly uses real Swift concurrency for MainActor scheduling.
• Removed misleading WASM/Embedded fallbacks for sleep, background, and delay; those APIs are now omitted there rather than silently providing incorrect semantics. main remains available on full-runtime WASM but is omitted for Embedded Swift.
• Reworked the Xcode test setup so SwiftPM owns the unit-test target while the Xcode project adds UI tests, eliminating duplicate CompatibilityTests.xctest products and exposing parameterized cases in the Test Navigator.
• Expands UI coverage across the demo tabs and adds focused unit coverage for high-value gaps.
• Targets v1.19.0 to reflect the broader testing/concurrency cleanup while remaining source-compatible for normally supported platforms.

Validation before merge

• Run swift test and confirm all reusable module parameter cases pass.
• Run the shared CompatibilityTest Xcode scheme and confirm both package tests and CompatibilityUITests pass.
• Re-run code coverage after the expanded UI and focused unit tests.
• Run supported-platform / Swift Package Index validation before tagging v1.19.0.

Follow-up

After release, Device can import CompatibilityTesting and replace its duplicated module-test adapter with ModuleTestEntry.