Work on max_cliques()

[maelle]

I am using Jarl's new unused_object check, that drew my attention to this function.

[maelle]

this tmpfile was not returned!

[maelle]

apparently not used

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if caabe13 is merged into main:

• ✔️as_adjacency_matrix: 774ms -> 775ms [-2.16%, +2.36%]
• ✔️as_biadjacency_matrix: 771ms -> 765ms [-2.22%, +0.63%]
• ✔️as_data_frame_both: 1.49ms -> 1.5ms [-1.5%, +2.34%]
• ✔️as_long_data_frame: 3.92ms -> 4.04ms [-2.34%, +8.56%]
• ✔️es_attr_filter: 2.93ms -> 2.94ms [-2.93%, +4.08%]
• ✔️graph_from_adjacency_matrix: 126ms -> 126ms [-2.94%, +1.98%]
• ✔️graph_from_data_frame: 3.43ms -> 3.42ms [-1.89%, +1.52%]
• ✔️vs_attr_filter: 1.64ms -> 1.65ms [-2.71%, +3.46%]
• ✔️vs_by_name: 1.14ms -> 1.12ms [-6.17%, +1.74%]
  Further explanation regarding interpretation and methodology can be found in the documentation.