tsort: drastically reduce memory copies

[tertsdiepraam]

To reduce the copying happening in tsort, we can load the entire input in memory and only refer to slices within that input instead of allocating a String for each occurrence of a node.

cc @anastygnome

On my input generated with:

import random

random.seed(0)

N = 10000
for i in range(100*N):
    a = random.randint(0,N)
    b = random.randint(0,N)
    if a != b:
        print(f"{min(a, b)} {max(a, b)}")

The time measured with hyperfine drops from ~2.3 seconds to ~1.6 seconds.

[anastygnome]

Nice, please set a fixed seed for reproducibility tho :)

[tertsdiepraam]

Fair :)