Use symplectic CSS parity check matrix

[perlinm]

Swaps the order of the X and Z sectors of the CSS parity check matrix, which is consistent with the fact that the X sector comes first everywhere else in the code (the inconsistency before this PR was in fact a bug).

Also put H_x "on the bottom", for consistency with (among other sources)

• https://errorcorrectionzoo.org/c/galois_css
• https://arxiv.org/abs/2202.01702 (Eq. 15)
• https://arxiv.org/abs/2401.02911 (Eq. 1)