Zero-dependency backend by default

[bwasti]

Right now there is a hard dep on arrayfire, which can be a nightmare to install. The plan is to instead ship two bindings: 1 array fire binding and 1 zero-dep binding. On program load, the array fire binding with be loaded, and if it fails, the other binding will be loaded.

Hopefully we can phase out installation pain entirely! :)

• Prototype a statically built OneDNN backend for flashlight https://github.com/bwasti/flashlight/tree/onedenn
• Build zero-dep backend in GitHub actions
• Fixup OneDNN to support all operations
• Change shumai binding logic to support fallbacks