unused import: `Polynomial`

When running:
```
$ RAYON_NUM_THREADS=8 cargo test -j 8
```

I get:
```
warning: unused import: `Polynomial`
--> tests/mse_e2e.rs:7:31
|
7 | use chipmunk_code::{KahePoly, Polynomial};
| ^^^^^^^^^^
|
= note: `#[warn(unused_imports)]` (part of `#[warn(unused)]`) on by default
```

More details of my testing set up and script in https://collective.flashbots.net/t/testing-panetiere/5868

Open tests/mse_e2e.rs at the reported import and run RAYON_NUM_THREADS=8 cargo test -j 8 to reproduce the warning. Remove the unused Polynomial import, then rerun the command and confirm the unused-import warning is gone.

Written by the indexing model from the issue text.