Make list.unique logarithmic instead of quadratic

[radekm]

Fixes #667. New list.unique implementation uses gleam/set to detect whether item has already been seen. New list.unique implementation uses gleam/dict to detect whether item has already been seen (it can't use gleam/set because that would create import cycle).

[lpil]

Thank you 💜

[radekm]

But unfortunately there's an import cycle.

The import statements for these modules form a cycle:

    ┌─────┐
    │     gleam/result
    │     ↓
    │     gleam/set
    │     ↓
    │     gleam/list
    └─────┘

[lpil]

Looks like you have a compile error!

[radekm]

So I have to come up with a different solution