Remove `sortedcontainers` dependency from pixi.toml

> The `pixi.toml` looks good! (only question is about `sortedcontainers`, which is a dependency but not used anywhere in the > project - but that's not from this PR)

_Originally posted by @VeckoTheGecko in https://github.com/Parcels-code/virtualship/issues/342#issuecomment-5612506534_

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`sortedcontainers` is an unused dependency, remove?
            