[BUG] Investigate potential compilation issues related to overloading `Base.cat`

[mtfishman]

@amilsted reported that as of this PR to NDTensors.BlockSparseArrays: ITensor/ITensors.jl#1579 loading NDTensors.jl/ITensors.jl along with DifferentialEquations.jl causes huge compile times. That might also be related to https://itensor.discourse.group/t/linearmaps-and-itensors-incompatibility/2216.

For NDTensors.jl/ITensors.jl, that issue should get fixed by ITensor/ITensors.jl#1601, since that PR removes BlockSparseArrays.jl from NDTensors.jl in favor of the version in this repository. We need to check if this package has the same problem, and if so rewrite it to avoid that problem.

See also ITensor/SparseArraysBase.jl#25.