[Meta] Migration to custom Tensor/Matrix interface and DROP S4TF Tensor and dependency

Removing all S4TF dependency will enable immediate revival of SwiftFusion since most codepath only use a fraction of the `Tensor` interface.

Issues I have on file (TODO: file them as issues)
1. math functions like `sin` needs replacement into their Swift-numerics counterpart
2. `swift-numerics` does not have `@differentiable`, need custom VJPs
3. `matmul` need hand implementation
4. `pinv` uses SVD in S4TF, need to be replaced

Possible solution directions:
- Handcraft usable but not great stuff for now to keep it together
- Move to SwiftRT?

supersedes #274