fix: Ability needs PartialOrd, not Ord

[tennox]

(as far as I understand)
Abilities can be compared, but aren't necessarily related. Nor do they have a 'total order'

Description

Given my simple example, where abilities have no hierarchy/relation:

#[derive(PartialEq, Eq, Clone, Debug)]
pub enum StorageAction {
    Read,
    Store,
    Pin,
}
impl Ability for StorageAction {}

Ord would require me to do this hack, pretending an ability is Less, which only works because Abilities are currently only compared via >=.

impl Ord for StorageAction {
    fn cmp(&self, other: &Self) -> Ordering {
        if self == other {
            Ordering::Equal
        } else {
            Ordering::Less
        }
    }
}

Correct, I think, would be PartialOrd:

impl PartialOrd for StorageAction {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        if self == other {
            Some(Ordering::Equal)
        } else {
            None
        }
    }
}

Of course, introducing hierarchy still works.

Type of change

• Bug fix (non-breaking change that fixes an issue)

Test plan (required)

I cargo buil[t] and cargo test[ed] 💁

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.44%. Comparing base (83528cc) to head (de24d0c).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #129      +/-   ##
==========================================
- Coverage   62.12%   60.44%   -1.68%     
==========================================
  Files          24       24              
  Lines         895      890       -5     
  Branches      214      233      +19     
==========================================
- Hits          556      538      -18     
+ Misses        196      190       -6     
- Partials      143      162      +19     

Files	Coverage Δ
ucan/src/capability/semantics.rs	47.52% <ø> (-0.52%)	⬇️

... and 14 files with indirect coverage changes