replace rng with deterministic indexer

[yoshuawuyts]

Closes #85. Additionally it also significantly simplifies our iteration logic by baking it into the Indexer struct directly:

// before
let len = this.streams.len();
let r = this.rng.generate(len as u32) as usize;
for index in (0..len).map(|n| (r + n).wrapping_rem(len)) { ... }

// after
for index in this.indexer.iter() { ... }

Performance

The numbers overall seem pretty comparable, but they spiked a bit on non-allocating APIs which are otherwise fairly simple. impl Race for array showed one of the bigger changes:

❯ critcmp main patch
group             main                    patch
-----             ----                    -----
array::race 10    1.22   652.2±24.21ns    1.00   535.9±31.39ns
array::race 100   1.52      4.8±0.27µs    1.00      3.2±0.02µs
array::race 1000  1.07     28.4±0.56µs    1.00     26.6±0.58µs

[matheus-consoli]

I like how this simplifies the iteration, and the strategy seems to make sense to me!

Once we fix the offset increment, we should be good to go

implemented feedback

[matheus-consoli]

This looks great!

[eholk]

Does it make sense to try to save where we ended up last time and pick up from there?