Limit get_block_id transaction hash count to prevent stack overflow

[MoneroOcean]

Motivation

• Prevent a denial-of-service crash caused by parsing untrusted block blobs with an excessive number of tx_hashes, since get_block_id reaches Merkle tree hashing that uses stack-allocation in tree_hash.

Description

• Add a defensive cap MAX_BLOCK_ID_TX_HASHES = 65535 in src/main.cc and return an error when b.tx_hashes.size() exceeds this limit before calling get_block_hash, preserving normal behavior for typical blocks.

Testing

• Ran npm test in the environment, which failed due to a network/npm registry 403 Forbidden error fetching the bech32 dependency so no project tests executed successfully.

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Codex Task