EIP-4881: Add merkle tree interface (#11597)

* Add merkle tree interface

* Run gazelle

Co-authored-by: Nishant Das <nishdas93@gmail.com>

beacon-chain/cache/depositsnapshot/BUILD.bazel

@@ -0,0 +1,8 @@
+load("@prysm//tools/go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["merkle_tree.go"],
+    importpath = "github.com/prysmaticlabs/prysm/v3/beacon-chain/cache/depositsnapshot",
+    visibility = ["//visibility:public"],
+)

beacon-chain/cache/depositsnapshot/merkle_tree.go

@@ -0,0 +1,19 @@
+package depositsnapshot
+
+const (
+	DepositContractDepth = 32 // Maximum tree depth as defined by EIP-4881.
+)
+
+// MerkleTreeNode is the interface for a Merkle tree.
+type MerkleTreeNode interface {
+	// GetRoot returns the root of the Merkle tree.
+	GetRoot() [32]byte
+	// IsFull returns whether there is space left for deposits.
+	IsFull() bool
+	// Finalize marks deposits of the Merkle tree as finalized.
+	Finalize(deposits uint, depth uint) MerkleTreeNode
+	// GetFinalized returns a list of hashes of all the finalized nodes and the number of deposits.
+	GetFinalized(result [][32]byte) ([][32]byte, uint)
+	// PushLeaf adds a new leaf node at the next available Zero node.
+	PushLeaf(leaf [32]byte, deposits uint, depth uint) MerkleTreeNode
+}