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/core/constants.rs

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright (c) 2023-2025 Matter Labs
+
+//! Constants used throughout the application
+
+/// Maximum number of retry attempts for fetching proofs
+pub const MAX_PROOF_FETCH_RETRIES: u32 = 3;
+
+/// Default delay between retries (in milliseconds)
+pub const DEFAULT_RETRY_DELAY_MS: u64 = 1000;
+
+/// Default timeout for HTTP requests (in seconds)
+pub const DEFAULT_HTTP_REQUEST_TIMEOUT: u64 = 30;
+
+/// SGX hash size in bytes
+pub const SGX_HASH_SIZE: usize = 32;
+
+/// TDX hash size in bytes
+pub const TDX_HASH_SIZE: usize = 48;