Bun has an open PR adding shared-memory threads to JavaScriptCore

Bun has an open pull request adding shared-memory threads to JavaScriptCore that allows running functions on separate cores within the same JavaScript heap without message passing or structured cloning. The new `Thread` API enables direct function execution across cores with access to closures and shared objects, simplifying parallel programming compared to traditional Web Workers. The implementation passes test suites with all JIT tiers executing without a global lock, though the PR is still in development and may never merge.