starknet_api: add DeployAccount v4 transaction type (Blake2 address derivation)

[ron-starkware]

Stack — part 3 of 9 (base: #14812). Targets 0.14.5.

Adds DeployAccount version 4: v3's exact field set, with the contract address derived by BLAKE2s + the Pedersen-image escape instead of Pedersen. The version felt is the scheme signal; v1/v3 keep deriving with Pedersen indefinitely, so there is no flag day and no stranded counterfactual address.

• DeployAccountTransactionV4 / RpcDeployAccountTransactionV4 + the enum variants.
• The v4 transaction hash is the v3 Poseidon layout with version felt 4 and the escaped address — no new hash function, in Rust or in Cairo.
• DeployAccountTransaction::address_derivation_hash() (V1/V3 → Pedersen, V4 → Blake2) is the single scheme-selection point; no caller hand-picks a scheme for a versioned transaction.
• Every serialization surface: RPC "0x4", protobuf DeployAccountV4 + the mempool/consensus/sync oneofs, storage discriminant V4 = 2, cende "0x4", the test-instance registry.

Fail-closed: blockifier's version allowlist still rejects v4 (#14815 enables it), and the gateway's stateful validation fully executes deploy-accounts, so v4 cannot be ingested from this PR alone.

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• starknet_os_flow_tests: prove a block with a DeployAccount v4 end-to-end #14819
• apollo_starknet_os_program,starknet_os: add the deploy_v2 syscall to the OS #14818
• blockifier: add the deploy_v2 syscall (Blake2 contract address derivation) #14817
• apollo_http_server,apollo_gateway_types: accept DeployAccount v4 at the gateway #14816
• blockifier: enable DeployAccount v4 execution #14815
• starknet_os: support DeployAccount v4 Blake2 address derivation in the OS #14814
• starknet_api: add DeployAccount v4 transaction type (Blake2 address derivation) #14813 👈 (View in Graphite)
• starknet_api: escape the Pedersen image in Blake2 contract address derivation #14812
• starknet_api: make contract address derivation hash-pluggable #14811
• main

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