Add a Full SWE solver

[lrntct]

This would allow more complex flows to be modeled (like dam break), albeit with an additional computational cost.
An explicit solver on a staggered grid would integrate nicely with the current code.

Potential candidates:

• https://www.mdpi.com/2311-5521/5/3/149
• https://www.sciencedirect.com/science/article/pii/S259003742100039X
• https://link.springer.com/article/10.1007/s40808-025-02566-x