This makes more dependencies lazy. This has a practical effect of
reducing the number of dependencies that need to be downloaded when
running certain zig build steps.
This is all limited because we're blocked on an upstream Zig issue:
https://github.com/ziglang/zig/issues/21525 This prevents us from
fully avoiding downloading many dependencies, but at least they're
relatively small.
One major improvement here is the usage of `lazyImport` for
`zig-wayland` that prevents downloading `zig_wayland` unconditionally on
all platforms. On macOS, we don't download this at all anymore.
Another, weirder change is that all our transitive dependencies are now
marked lazy (e.g. glslang's upstream source) even if the glslang build
always requires it. This was necessary because without this, even if we
simply referenced glslang in the root build.zig, it would force the
source package to download unconditionally. This no longer happens.
This adds a new script `update-mirror.sh` which generates the proper
blob format for R2 (or any blob storage) to mirror all of our
dependencies.
It doesn't automate updating build.zig.zon but on an ongoing basis this
should be easy to do manually, and we can strive to automate it in the
future.
I omitted iTerm2 color themes because we auto-update that via CI and
updating all of the machinery to send it to our mirror and so on is a
pain. Additionally, this doesn't mirror transitive dependencies because
Zig doesn't have a way to fetch those from a mirror instead (unless you
pre-generate a full cache like packagers but that's not practical for
day to day development).
It's hugely beneficial just to get most of our dependencies mirrored.
