Memory error for transport model using scipy solver

I tried using the scipy solver with @sharwaridixit's transport model, and got this rather alarming error:

`numpy.core._exceptions._ArrayMemoryError: Unable to allocate 40.2 GiB for an array with shape (16, 16, 7, 7, 41, 41, 16, 16) and data type float64`

It's specifically being thrown by [this line](https://github.com/EnergySystemsModellingLab/MUSE_OS/blob/4c0b53dc4ca1857689d4a8c177f8b9c691843aad/src/muse/constraints.py#L853) in the calculation of the constraint matrix. I'm guessing there's a bug somewhere that's accidentally duplicating all the dimensions of an array, but I'd need to investigate further