Squashfs support for packages

[martenrichter]

This is a pull request to document the current experimental work for squashfs support.
It is not yet ready to be merged, and it will only be worthy of a merge once it is determined that a substantial performance advantage is achieved, which has yet to be determined.

Its purpose is currently to make sure that it does not go in the wrong direction.

[martinRenou]

Thanks!! Where you able to see a speedup locally?

[martenrichter]

I am not there yet.
I still have to implement the squashfs support in mambajs (which requires a major change in its inner logic, first quick idea is to mount the sqfs and use symlinks).
And I also have to enable wasmfs support in the kernel builds (where I am struggling to get a local setup of the recipes).
So there is still a long way to go until I know. And then one can decide about the details.