perf(l1): optimize Nibbles::skip_prefix to avoid tail allocation and remove redundant clone

[GarmashAlex]

Motivation

Minor inefficiencies: unnecessary clone() in get_path() and allocations in Nibbles::skip_prefix()

Description

• Replace self.child.clone().compute_hash() with self.child.compute_hash() in ExtensionNode::get_path() to avoid an unnecessary Arc clone. NodeRef::compute_hash(&self) already memoizes and requires no ownership.
• Reimplement Nibbles::skip_prefix() using drain(..plen) to move the matched prefix into already_consumed without allocating a new Vec for the remaining tail. Semantics are preserved: data becomes the same tail and already_consumed gains the same bytes previously appended from prefix.data.