`Duration` doesnt implement `Eq` trait

[MbBrainz]

I guess this would be nice to have. Is there a reason for not implementing it?

[maurolacy]

Probably nobody needed it so far. Go ahead and submit a PR if you want.

[webmaster128]

Through #[cw_serde] it derives PartialEq. But because of that we don't see a clippy warning to also add Eq. Feel free to add.