optimize endpoints Targets struct

[dongjiang1989]

What would you like to be added:

 it may call ParseAddr many times for the same target.
So let's give us one more chance to avoid that. I have an other idea.

Wdyt about converting Target from a string to a struct with a string and Addr* ?
It would mean it may use Addr when it's relevant and keep string comparison when it's not an IP ?

Originally posted by @mloiseleur in #4351 (comment)

Why is this needed:

change Targets from []string to []Target

type Target struct {
	Addr netip.Addr
	Raw  string
}
// Targets is a representation of a list of targets for an endpoint.
type Targets []Target

Tasks

Beta Give feedback

1. Fix(ipv6): support ipv6 shortener and expander equal #4351
   approved cncf-cla: yes lgtm ok-to-test size/M +5
   
2. feat(endpoint): optimize endpoint Targets struct #4379
   cncf-cla: yes needs-ok-to-test size/XXL +3

[dongjiang1989]

/cc @mloiseleur
I'll add a follow-up PR to optimize it.