[WIP] Initial wrapper for blasfeo.

[apozharski]

This is properly beginning to interface blasfeo to julia. It should work with the current blasfeo_jll but I only tested it with the version built from the branch in this PR to Yggdrasil: JuliaPackaging/Yggdrasil#13933

Current design decisions

• Implement four new types:
  • BlasfeoDvec <: AbstractVector{Cdouble}
  • BlasfeoSvec <: AbstractVector{Cfloat}
  • BlasfeoDmat <: AbstractMatrix{Cdouble}
  • BlasfeoSmat <: AbstractMatrix{Cfloat}
    and implement the required methods for basic functionality.
• These structs are mutable so we can pass pointers to them to blasfeo_* ccalls, but all fields are const as users shouldn't manually change the values in them.
• ...

Functions already using blasfeo specializations:

• Constructors for matrices/vectors of fixed size and from Matrix/Vector
• scalar get_index
• scalar set_index!
• fill!
• copy

TODO:

• Implement specializations for level1 blas operations
• Implement specializations for level2 blas operations
• Implement specializations for level3 blas operations
• We may want to hook in to some of the lapack operation specializations in julia, but I will probably only do this as needed

Marked WIP because I at least want to finish the lvl1 blas and lvl2 blas specializations before we merge this.