zipfs: port from afero

[progrium]

We'll be using zip as our starting general archive format. If we need to aggregate files into a single blob, zip is such a widely deployed format that there isn't a reason to invent one. We'll already be using it to bundle compressed files with executables as a polyglot file a la redbean for our compiler. We'll probably use it to export/download parts of the Wanix filesystem, as well as include certain filesets in the bundled bootloader.

And leaning into our filesystem abstraction, it will likely be helpful to have a zipfs. One first usecase is to allow user zip files on the filesystem to be automatically explored (similar to Windows). In the case of our compiler build, as it is also a zipfile containing the precompiled standard library, zipfs could be used to just mount the file instead of extracting and writing files out to be used, then deleting them. Not a material benefit, but seems cleaner.

A simply read-only zipfs using the Go standard library's zip package is already implemented in afero and would be trivial to port to our FS abstraction.