gnosis / dex-services / 5556

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Custom TokenPairRange.arbitrary implementation with 30 hops bound (#1552)

Fixes the recent fuzzer crashes by implementing arbitrary of TokenPairRange with a hard cap of 30. This is fine, as the query params get sanitized [here](https://github.com/gnosis/dex-services/blob/db7b913f7/price-estimator/src/models/query.rs#L92-L98) and so we never create a TokenPairRange that is larger.

Not sure if on top of this it makes sense to limit the hops in a TokenPairRange contructor. Not limiting 0 hops as this is still possible from an API perspective and thus should probably be fuzzed as well.

### Test Plan
Unpack [crash.bin.zip](https://github.com/gnosis/dex-services/files/5582570/crash.bin.zip) and run

```
cargo +nightly fuzz run pricegraph ~/Downloads/crash.bin
```

And see no more crash.

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