fix: building vertices not working on Safari and improve stop button

[nicoloboschi]

This PR addresses two problems:

1. the current client implementation to read chunks from the response using Fetch API is not standard and not compatible with Safari (and probably others). The right way is to use body.getReader() which has much larger support
2. The Stop button stops the build but it appears to not be working since no feedback is given to users

[github-actions]

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_{Last Modified at 27 Aug 24 11:17 UTC}

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