Feat: statically link top-layer dependencies

[robbielyman]

• [x] use build.zig.zon to capture and pin dependency commits
• [x] convert build systems of top-level dependencies to `build.zig
• [x] add repos for top-level dependencies as submodules
• [x] test on Linux (help wanted! otherwise I won't start working on it till next week. but you'll have to futz with build.zig some, sorry)
• [ ] set up github actions CI I'm gonna merge and then revisit this