fix: untrack $inspect.with and add check for unsafe mutation

[paoloricciuti]

Closes #16156

It's important for inspect to be pure both because it's not there in production and because being sync it can tear the graph. While writing the test i've also noticed that if you did this

$inspect(a).with((...args)=>{
    console.log(...args);
    b;
});

b was also a dependency of the whole inspect (and it was not even showing up in the logs) so i untracked the inspector call (keeping the snapshot outside of the untrack to deeply read the value)

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Preview: https://svelte-dev-git-preview-svelte-16209-svelte.vercel.app/

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