Add scaling experiments for data structures paper 10.1080/17445760.2023.2266875

• Adds the scaling experiments at apps/2023-data-structures
• Adds a new Torus map which is a simplified version of the Tokamap map (4b6ce45b)
• Fixes an issue with the Tokamak map, where the poloidal angle was determined even at poloidal radius 0 (caused NaN values) (d2f5891a)
• Introduces a few new forms (which are deprecated by the gen. operators but kept for reproducibility):
  • n1e1 \mathrm{curl}\thinspace\mathrm{curl}\thinspace\boldsymbol{u} + \boldsymbol{u}, affine and blending
  • n1e1 linear form, blending
  • p1 diffusion q2, blending
• Includes some scalability improvements:
  • Chebyshev smoother: Temporary vectors can be supplied from outside (to allow reuse) (9f5191af)
  • n1e1 hybrid smoother: Temporary n1e1 vector can be supplied from outside (to allow reuse) (15f4b7a5)
  • FMG: Number of V-cycles can be specified for each level individually (91da7e79)