PDEs to be implemented

[termoshtt]

• Kuramoto-Sivashinsky (1D) import KSE from rust-spectral #45
• Swift-Hohenberg (1D) Swift-Hohenberg equation #74
• Complex Ginzburg-Landau (1D)
• KdV (1D)
• Gray-Scott (2D)
• Navier-Stokes (2D, 3D)