Mark public API with public keyword

[mofeing]

Now that API stabilization is coming closer and closer and users are starting to run with some problems on what should be used or not, we should start marking public API with the new public keyword which landed in Julia 1.11.

https://docs.julialang.org/en/v1/base/base/#public

• Exported symbols are automatically public
• There are some symbols which we want them to be public (i.e. users should not be afraid of using them) but not export them automatically (i.e. you need to access by explicit import or Tenet.whatever access). Those are the ones we must mark them as public.

Compat.jl provides the @public macro which acts as a no-op in Julia 1.10