User reported that running next repo using turbopack doesn't work with mirrord

webpack --> mirrord exec -f .mirrord/mirrord.json -- next dev -p 4004
  turbopack --> mirrord exec -f .mirrord/mirrord.json -- next dev --turbopack -p 4004

We had this issue in the past and thought same workaround would work but when running from next cli you can't really add the workaround configuration.

I thought the fix would be in Vercel's Turborepo side but they didn't allow us to include mirrord env variables.

This leads me to the following idea - instead of saving settings inside env variables and trust it'd propagate between sub processes, we will use a const fd + memfd to store the data.

On mirrord config access -> check if our const 94838 FD is valid, if it is, check if it has magic in first 4 bytes, if it does, load encoded settings from there -> can repeat and iterate on FDs in case our FD is used already for other means -> if we can't find in fd fallback to env.