[WIP] [NDTensors] Excise libraries

[mtfishman]

This PR deletes a big set of submodules of NDTensors and moves them to separate repositories, for example NDTensors.BlockSparseArrays has been moved to the new BlockSparseArrays.jl repository. Most will be unregistered (potentially interdependent) packages for the time being, while TypeParameterAccessors.jl will be registered since it is used extensively throughout NDTensors.jl and also is used by some of the new packages.

So far most of the packages are kept as-is, however GradedAxes has been renamed to GradedUnitRanges.

I followed the instructions here to preserve the git history of the subfolders.

To-do:

• Register TypeParameterAccessors.jl so it can be used as a dependency of NDTensors and also other packages.
• Delete code loading and testing workflows related to the excised modules.
• Rewrite code in NDTensors that was depending on DiagonalArrays, so that it can be removed as a dependency.
• Many of the new packages aren't functional yet so I won't merge this until that is fixed. The goal will be for them to all have their own CI with tests of downstream packages. At first they won't be registered, but we will configure them to install unregistered dependencies automatically with a [sources] section in their Project.toml (see https://pkgdocs.julialang.org/v1/toml-files/#The-%5Bsources%5D-section).

The packages should be set up in a uniform way using ITensorPkgSkeleton.jl. The following packages have been set up based on the code removed in this PR:

• BlockSparseArrays.jl
• BroadcastMapConversion.jl
• DiagonalArrays.jl
• GradedUnitRanges.jl
• LabelledNumbers.jl
• NamedDimsArrays.jl
• NestedPermutedDimsArrays.jl
• SparseArraysBase.jl
• SymmetrySectors.jl
• TensorAlgebra.jl
• TypeParameterAccessors.jl
• UnallocatedArrays.jl
• UnspecifiedTypes.jl

Here are package extensions that need to be set up for compatibility with NDTensors.jl and ITensors.jl, which will be addressed in future work:

• NamedDimsArraysITensorsExt (Not complete, but tracking in Create NamedDimsArraysNDTensorsExt and NamedDimsArraysITensorsExt NamedDimsArrays.jl#3.)
• NamedDimsArraysNDTensorsExt (Not complete, but tracking in Create NamedDimsArraysNDTensorsExt and NamedDimsArraysITensorsExt NamedDimsArrays.jl#3.)

Other libraries to split off in future PRs are (these are being used in some tests which requires loading NDTensors as a test dependency):

• AMDGPUExtensions.jl
  
• BackendSelection.jl
• CUDAExtensions.jl
• GPUArraysCoreExtensions.jl
• GPUArraysTestUtils.jl
• MetalExtensions.jl