Bug Description

When calling 'steadystate()' for large Hilbert space sizes with operators built out of DIA, we often hit a memory error. This line:

Seems to be the culprit. Either needs an option to capture other sparse formats, or convert to CSR (which is done later in the steadystate function for DIA anyway?)

Code to Reproduce the Bug

Code Output

Expected Behaviour

Sparse problems shouldn't run out of memory

Your Environment

QuTiP Version:      5.3.0.dev0+8d2e163
Numpy Version:      1.26.4
Scipy Version:      1.14.1
Cython Version:     0.29.36
Matplotlib Version: 3.5.0
Python Version:     3.10.12
Number of CPUs:     12
BLAS Info:          INTEL MKL
INTEL MKL Ext:      /home/neill/qutip-dev310/lib/libmkl_rt.so.2
Platform Info:      Linux (x86_64)
Installation path:  /mnt/d/github/qutip/qutip

Additional Context

No response