refactor(verify-era-proof-attestation): modularize and restructure proof verification logic

- Split `verify-era-proof-attestation` into modular subcomponents for maintainability.
- Moved client, proof handling, and core types into dedicated modules.

bin/verify-era-proof-attestation/src/client/json_rpc.rs

@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright (c) 2023-2025 Matter Labs
+
+use url::Url;
+use zksync_basic_types::{L1BatchNumber, H256};
+use zksync_types::L2ChainId;
+use zksync_web3_decl::{
+    client::{Client as NodeClient, L2},
+    error::ClientRpcContext,
+    namespaces::ZksNamespaceClient,
+};
+
+use crate::error;
+
+/// Trait for interacting with the JSON-RPC API
+pub trait JsonRpcClient {
+    /// Get the root hash for a specific batch
+    async fn get_root_hash(&self, batch_number: L1BatchNumber) -> error::Result<H256>;
+    // TODO implement get_tee_proofs(batch_number, tee_type) once https://crates.io/crates/zksync_web3_decl crate is updated
+}
+
+/// Client for interacting with the main node
+pub struct MainNodeClient(NodeClient<L2>);
+
+impl MainNodeClient {
+    /// Create a new client for the main node
+    pub fn new(rpc_url: Url, chain_id: u64) -> error::Result<Self> {
+        let chain_id = L2ChainId::try_from(chain_id)
+            .map_err(|e| error::Error::Internal(format!("Invalid chain ID: {}", e)))?;
+
+        let node_client = NodeClient::http(rpc_url.into())
+            .map_err(|e| {
+                error::Error::Internal(format!("Failed to create JSON-RPC client: {}", e))
+            })?
+            .for_network(chain_id.into())
+            .build();
+
+        Ok(MainNodeClient(node_client))
+    }
+}
+
+impl JsonRpcClient for MainNodeClient {
+    async fn get_root_hash(&self, batch_number: L1BatchNumber) -> error::Result<H256> {
+        let batch_details = self
+            .0
+            .get_l1_batch_details(batch_number)
+            .rpc_context("get_l1_batch_details")
+            .await
+            .map_err(|e| error::Error::JsonRpc(format!("Failed to get batch details: {}", e)))?
+            .ok_or_else(|| {
+                error::Error::JsonRpc(format!("No details found for batch #{}", batch_number))
+            })?;
+
+        batch_details.base.root_hash.ok_or_else(|| {
+            error::Error::JsonRpc(format!("No root hash found for batch #{}", batch_number))
+        })
+    }
+}