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

[ProfFan]

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