Cross-platform test commands

[jsmaxi]

https://docs.minaprotocol.com/zkapps/writing-a-zkapp/introduction-to-zkapps/how-to-write-a-zkapp

In the Sudoku example, the test commands do not work reliably across all platforms and terminals (File not found - *.test.js, find: missing argument to -exec).
Recommendation: replace them with these cross-platform test commands:

    "test": "npm run build && node --test build/src",
    "testw": "npm run build && node --test --watch build/src",