All4x4Tables: update after #281 (#294)

This PR:

**1.** Adds 4 more cancellative magmas that were found through
hand-guided search and which refute 31 of the 29688 implications still
open after #281, bringing down the number to 29657. The idea was to find
for cancellative magmas that specifically fail to satisfy large
one-variable laws. The addition of the new magmas also results in a
slightly better plan (with fewer Lean checks required).

**2.** Re-runs the transitive closure pruning using the large number of
recently proved implications. This further pushes down the number of
explicitly proven implications from 604701 to 581162 .

**3.** Adds a minor QoL improvement to variable counting in
`finite_magma_tools`, which makes it more useful for #278 -style
experimentation.