fix: build_wasm copy executor to defaults

[aoyako]

Context

Fix the build_wasm.sh script to copy generated wasm files to the defaults folder. The issue is currently reproducible on macOS.

Checklist

• [ ] I've read CONTRIBUTING.md.
• [ ] (optional) I've written unit tests for the code changes.
• [ ] All review comments have been resolved.
• [ ] All CI checks pass.