Use zstd for compression of blobs

[eestrada]

Example of how to build zstd for a zig project: https://github.com/allyourcodebase/zstd

Currently, zig is not yet v1.0, so its build system is in constant flux. Do not directly depend on the package above (which itself is just a wrapper around the actual zstd repo). Besides it is created for version 0.14.0 of zig and the current version is 0.15.1, so it probably isn't compatible anymore anyway.

Instead use it's build.zig and build.zig.zon files as inspiration and reference for implementing a similar build process in Havarti's build.zig and build.zig.zon files.