Add overrides for the iterator methods that do not get the key

Materializing the keys out of the compact sequences is a significant part of the work. But in some cases you only need the value.

There should be variants of the 2 iter methods that return (Offset, Value) instead of (Offset, Key, Value). That would be faster and fewer mallocs.

Start by locating the two iterator methods referred to in the issue and trace how compact sequences materialize keys. Compare their existing return values and identify the corresponding variants that return (Offset, Value); done means both variants avoid unnecessary key materialization while preserving iterator behavior and reducing allocations.

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