SCORU: benchmark cost constants

In order to complete the carbonation of SCORU operations (see #3290 (closed)), we need to benchmark the constants introduced in Sc_rollup_costs.Constants.

• cost_add_message_base
• cost_add_message_per_byte
• cost_add_inbox_per_level
• cost_update_num_and_size_of_messages
• cost_decoding_contract_optimized
• cost_decoding_key_hash_optimized
• cost_encode_string_per_byte
• cost_serialize_state_hash
• cost_serialize_commitment_hash
• cost_serialize_commitment
• cost_serialize_operation_hash
• cost_serialize_nonce