RRuleSetIter: removed lifetimes and added from_str example

[AlbanWS]

This is just between a feature and a fix.

In my use-case, i have to store a RRuleSetIter inside an object up to keep the current state of the iterator and not recreate the iterator again and again

Therefore, it was not possible due to the lifetime of RRuleSetIter, currently :

pub struct Recurrent<'a> {
    rrule_iter: RRuleSetIter<'a>,
}

impl<'a> FromStr for Recurrent<'a> {
    type Err = RRuleError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let rrule = s.parse::<RRuleSet>()?;
        let iter: RRuleSetIter<'a> = rrule.into_iter();
        return Ok(Self {
            rrule_iter: iter,
        });
    }
}
 

Gives this error :

error[E0597]: `rrule` does not live long enough
  --> src/programs/module/recurrent.rs:17:38
   |
12 | impl<'a> FromStr for Recurrent<'a> {
   |      -- lifetime `'a` defined here
...
16 |         let rrule = s.parse::<RRuleSet>()?;
   |             ----- binding `rrule` declared here
17 |         let iter: RRuleSetIter<'a> = rrule.into_iter();
   |                   ----------------   ^^^^^ borrowed value does not live long enough
   |                   |
   |                   type annotation requires that `rrule` is borrowed for `'a`
18 |         return Ok(Self { rrule_iter: iter });
19 |     }
   |     - `rrule` dropped here while still borrowed

So, I removed the lifetimes, and the only real change is the in the struct IterInfo where the field rrule have to be a value and not a reference, and it has to be cloned on IterInfo::new.

Since it is also possible now, I implemented FromStr for RRuleSetIter in addition.

[fmeringdal]

Thanks for the contribution. LGTM!

Once the CI issues are resolved we can merge this

[AlbanWS]

Thanks for review, I reformatted the file who broke the CI.