Implement iterator deduplicator

[StephenButtolph]

Why this should be merged

Factored out of #3379.

How this works

While looking for the Next value - if the value was already seen, skip it. If the value wasn't seen, mark it as seen and stop iterating.

How this was tested

• Added unit test

[yacovm]

type deduplicator[T comparable] struct {
	Iterator[T]
	seen set.Set[T]
}

Wondering if it makes sense to just embed the iterator and drop Value and Release

[yacovm]

I works locally for me:

index b36c1e0a1..4ba769c12 100644
--- a/utils/iterator/deduplicate.go
+++ b/utils/iterator/deduplicate.go
@@ -8,7 +8,7 @@ import "github.com/ava-labs/avalanchego/utils/set"
 var _ Iterator[any] = (*deduplicator[any])(nil)
 
 type deduplicator[T comparable] struct {
-       it   Iterator[T]
+       Iterator[T]
        seen set.Set[T]
 }
 
@@ -16,13 +16,13 @@ type deduplicator[T comparable] struct {
 // been returned from [it].
 func Deduplicate[T comparable](it Iterator[T]) Iterator[T] {
        return &deduplicator[T]{
-               it: it,
+               Iterator: it,
        }
 }
 
 func (i *deduplicator[_]) Next() bool {
-       for i.it.Next() {
-               element := i.it.Value()
+       for i.Iterator.Next() {
+               element := i.Iterator.Value()
                if !i.seen.Contains(element) {
                        i.seen.Add(element)
                        return true
@@ -30,11 +30,3 @@ func (i *deduplicator[_]) Next() bool {
        }
        return false
 }
-
-func (i *deduplicator[T]) Value() T {
-       return i.it.Value()
-}
-
-func (i *deduplicator[_]) Release() {
-       i.it.Release()
-}

[StephenButtolph]

I removed this custom iterator implementation and reused Filter.

[StephenButtolph]

Embedding does work - but it has introduced subtle bugs in the past (because changing the signature of Next to NewNext or something wouldn't cause the code to fail to compile, but would cause the implementation to be wrong)...

This is why we use Unsafe.*Server rather than Unimplemented.*Server in our grpc services.

Side note - calling it Unsafe was ridiculous. I'll never understand decisions like that

[yacovm]

Reminds me of InsecureSkipVerify