Bump `engines` field to Node v16

Checklist

[x] I have ensured my pull request is not behind the main or master branch of the original repository.
[x] I have rebased all commits where necessary so that reviewing this pull request can be done without having to merge it first.
[x] I have written a commit message that passes commitlint linting.
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150 bumps the minimum required Node.js version to v10
151 bumps the minimum required Node.js version to v16
Future PRs will assume Node.js v16 at least (which has been EOL since a few months ago)

This updates the engines field to match.