Switch to @iarna/toml package with better TOML language features support

[jacob-8]

Fixes #1493 and allows Cloudflare Workers users and Netlify users to use features added to the TOML spec after v0.4.0 such as dotted keys like those described in https://developers.cloudflare.com/workers/cli-wrangler/configuration#service-workers

https://github.com/BinaryMuse/toml-node has gone stale at TOML spec v0.4.0
This PR switches to using https://github.com/iarna/iarna-toml as a lighter-weight, more up to date and equally used package.
https://github.com/LongTengDao/j-toml is slightly more up to date with the TOML spec (v1.0.0-rc.1 vs v1.0.0) but with very low usage and a bundle size 10x as large, I did not look into using it.

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