feat: implement PayloadProof function (#14356)

* feat: implement function `PayloadProof` to calculate proof of execution payload

* remove comments

* feat: implement function to compute field roots of

* feat: implement function to compute `BeaconBlock` field roots and add tests

* fix dependencies

* check if interface implements the assserted type

* fix: lint

* replace `ok != true` with `!ok`

* remove unused parameter from `PayloadProof`

* remove test and move `PayloadProof` to `blocks/proofs.go`

* remove `PayloadProof` from `fieldtrie`

* replace `fieldtrie.ProofFromMerkleLayers` with `trie.ProofFromMerkleLayers`

* Update container/trie/sparse_merkle.go

* update dependencies

---------

Co-authored-by: Radosław Kapka <rkapka@wp.pl>
Co-authored-by: Radosław Kapka <radoslaw.kapka@gmail.com>

container/trie/sparse_merkle.go

@@ -259,3 +259,18 @@ func (m *SparseMerkleTrie) NumOfItems() int {
 	}
 	return len(m.originalItems)
 }
+
+// ProofFromMerkleLayers creates a proof starting at the leaf index of the merkle layers.
+func ProofFromMerkleLayers(layers [][][]byte, startingLeafIndex int) [][]byte {
+	// The merkle tree structure looks as follows:
+	// [[r1, r2, r3, r4], [parent1, parent2], [root]]
+	proof := make([][]byte, 0)
+	currentIndex := startingLeafIndex
+	for i := 0; i < len(layers)-1; i++ {
+		neighborIdx := currentIndex ^ 1
+		neighbor := layers[i][neighborIdx]
+		proof = append(proof, neighbor)
+		currentIndex = currentIndex / 2
+	}
+	return proof
+}