graphs: implementation of linear-time algorithm for modular decomposition #16667

Job	Run time
test-new	13m 18s
test-mod (sagemath_categories-check)	6m 0s
test-long (src/sage/[a-f]*)	33m 22s
test-long (src/sage/[g-o]*)	35m 53s
test-long (src/sage/[p-z]*)	37m 40s
test-long (src/doc src/sage_docbuild src/sage_setup)	10m 37s
coverage-report	18m 49s
	2h 35m 39s

Provide feedback