fix: remove legacy import assertion unsupported by Node v22

[geigerzaehler]

I wasn’t able to build the project using Node v22 because it used the legacy import assertion syntax. Support for this was removed from Node. To fix this, I’m reading package.json as to not rely on JSON module support which may be unavailable on older Node versions (?).

I’m also fixing the Github workflows so that they actually run against different Node versions and we can discover this in the future.

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Latest commit: 0436e063e15389a4904cc0864fe71394e6e88601

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[benmccann]

ah. apparently assert is becoming with: https://github.com/nodejs/node/issues/51622