simple_cycles 的指数级运行时间 (含 length_bound (_bounded_cycle_search))

The graph contains exactly 2^t simple cycles, all of the length 2t+1 > k, so the search must terminate without output; total time = one delay period. The graphs are sparse, n=3t+1, m=4t+1, k=2t and the delay for `_bounded_cycle_search` should be at most quadratic in t. For graphs that are small and without an excessive number of valid cycles, the observed delay should stay close to zero.