Bound untrusted block tx_hashes before merkle hashing

[MoneroOcean]

Motivation

• Prevent untrusted/remote block templates from triggering unbounded merkle-tree scratch allocations (via tree_hash) that can exhaust the process stack and cause a denial-of-service.

Description

• Introduce MAX_BLOCK_TX_HASHES and return false from get_block_hashing_blob when b.tx_hashes.size() exceeds this limit to stop large attacker-controlled inputs from reaching tree_hash.

Testing

• Ran the project test command npm test, which failed in this environment due to registry access (403 Forbidden fetching dependency bech32), so automated tests could not complete successfully.

---

Codex Task