gnosis / dex-services / 5050

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use new transitive order iterator (#1386)

This PR makes use of the new transitive orders iterator method to implement the `pricegraph` API methods in a (hopefully) cleaner way.

### Test Plan

Refactoring, unit tests still pass without modification.

Benchmarks show no changes to the slower methods on overlapping orderbooks. There was some mild regression on benchmarks for the faster methods on reduced orderbooks. I suspect this is because we are filling and extra unneeded transitive order. For estimates that require very few transitive orders (for smaller sell amounts that get filled in the first few transitive orders) this extra overhead becomes more significant. Overall, this only affects the already very fast methods so I'm not worried.
<details><summary>Benchmarks</summary>

```
     Running target/release/deps/pricegraph-656df3332885b719
Gnuplot not found, using plotters backend
Pricegraph::read        time:   [7.2581 ms 7.2629 ms 7.2679 ms]                             
                        change: [-0.2522% -0.0369% +0.2010%] (p = 0.76 > 0.05)
                        No change in performance detected.
Found 8 outliers among 100 measurements (8.00%)
  2 (2.00%) low mild
  3 (3.00%) high mild
  3 (3.00%) high severe

Pricegraph::transitive_orderbook/5298183                                                                            
                        time:   [7.1418 ms 7.1496 ms 7.1590 ms]
                        change: [-0.4459% +0.4202% +1.0276%] (p = 0.40 > 0.05)
                        No change in performance detected.
Found 6 outliers among 100 measurements (6.00%)
  3 (3.00%) high mild
  3 (3.00%) high severe

Pricegraph::estimate_limit_price/100000000000000000                                                                             
                        time:   [61.611 us 61.697 us 61.788 us]
                        change: [+8.6387% +9.0841% +9.5049%] (p = 0.00 < 0.05)
                      ... (continued)

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