Make the Docker image cross-compile without QEMU emulation

[sandhose]

This does three things:

• Bump all dependencies & disable the pyo3 feature by default (because I had issues with old versions of maturin & openssl)
• Make the Docker image cross-compile without QEMU emulation
• Add a build cache on the Docker image

[clokep]

I'm not really sure how to test this -- should we kick off a manual build to see it work? (I'm unsure if that'll push the image / cause it to get used automatically.)

Overall it looks plausible though.

[sandhose]

I'm not really sure how to test this -- should we kick off a manual build to see it work? (I'm unsure if that'll push the image / cause it to get used automatically.)

You can try building the image locally for a foreign platform, e.g. docker build --platform=linux/arm64 ., and it should work if you have a recent enough docker?

[clokep]

Seemed to work OK.