LabelPair PartialOrd inconsistent with PartialEq

[rtimush]

Describe the bug
PartialOrd is implemented manually for prometheus::proto::LabelPair and it only compares the name. However, PartialEq is derived, so it checks all fields. This violates PartialOrd requirements (a == b if and only if partial_cmp(a, b) == Some(Equal)) and may cause issues if LabelPair is used in standard containers.

To Reproduce

let mut a = LabelPair::new();
a.set_name("name".to_owned());
a.set_value("a".to_owned());

let mut b = LabelPair::new();
b.set_name("name".to_owned());
b.set_value("b".to_owned());

assert!(a.cmp(&b) == Ordering::Equal);
assert_eq!(a, b) // fails

Expected behavior
Either PartialEq should be implemented manually to only compare the name field for consistency with PartialOrd, or PartialOrd should compare all fields. It's also worth mentioning in the docs if only name constitutes the equality, as it can be quite surprising.

Additional context
I had a bug because tried to put LabelPair into a BTreeSet.