Added 3D Shepp-Logan and array type modification

[hzarei4]

In this work, I developed this package to support 3D Shepp-Logan data. It is also optimized in case of speed and memory allocations. The user can now define which array type is needed and this function can return that defined type in the function input argument.

julia> @btime a = TestImages.shepp_logan(100, 100, 100);
  26.277 ms (67 allocations: 7.64 MiB)

julia> @btime a = TestImages.shepp_logan(100, 100, 1);
  251.000 μs (65 allocations: 83.50 KiB)

In addition, I tested with the Julia version 1.6.7 and it is compatible with this older Julia version.

With this machine hardware and software configuration:

julia> versioninfo()
Julia Version 1.10.4
Commit 48d4fd4843 (2024-06-04 10:41 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: 16 × 11th Gen Intel(R) Core(TM) i7-11700KF @ 3.60GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, rocketlake)
Threads: 16 default, 0 interactive, 8 GC (on 16 virtual cores)
Environment:
  JULIA_EDITOR = code