Fix: Implement ToOwned correctly

[NobodyXu]

To do that, we would need to update <leon::Tempalte as Clone>::clone to call .to_owned on Cow::Borrowed, which is a breaking change and would need documentation.

[NobodyXu]

Also, leon::Item can only contains & str, so even if we fix the implementation of <leon::Template as Clone>::clone, the leon::Template::items would still contains reference, not String.

To fix that, it has to be changed to Cow<'_, str>.

I didn't remember why we didn't use Cow<'_, str> @passcod .

leon/crates/leon/src/template.rs

Line 12 in 2209aba

pub enum Item<'s> {

[passcod]

Probably just missed it when refactoring

[NobodyXu]

Got it, I would just change it to Cow<'_, str> then