Add EIP-7702 (type 4) transaction support

[alisinabh]

https://eips.ethereum.org/EIPS/eip-7702

[Copilot]

Pull request overview

This PR adds support for Ethereum EIP-7702 “set-code” (type 4) transactions to the Ethers Elixir library, including authorization hashing/signing, JSON-RPC (de)serialization, and end-to-end test coverage.

Changes:

• Introduces Ethers.Transaction.Eip7702 plus authorization structs (Ethers.Authorization, Ethers.Authorization.Signed) and signing support via the signer behaviour.
• Extends Ethers.Transaction RPC mapping to include authorizationList and adds a public Ethers.sign_authorization/2 API.
• Adds comprehensive tests for decoding/encoding type-4 transactions and for signing/recovering authorizations.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/ethers/transaction_test.exs	Adds EIP-7702 transaction decode/encode and RPC map round-trip tests.
test/ethers/signer/local_test.exs	Adds deterministic fixtures for Signer.Local.sign_authorization/2.
test/ethers/authorization_test.exs	New unit tests for authorization creation, hashing, RLP, and authority recovery.
test/ethers_test.exs	Adds integration tests for Ethers.sign_authorization/2 and an EIP-7702 delegation lifecycle.
lib/ethers/transaction/eip7702.ex	New transaction type module implementing EIP-7702 fields and RLP encoding/decoding.
lib/ethers/transaction.ex	Adds authorization_list <-> authorizationList mapping and encoding/decoding helpers.
lib/ethers/signer/local.ex	Implements sign_authorization/2 for the local signer (when secp256k1 is available).
lib/ethers/signer/json_rpc.ex	Explicitly returns {:error, :not_supported} for authorization signing.
lib/ethers/signer.ex	Extends signer behaviour docs/callbacks to include sign_authorization/2.
lib/ethers/authorization/signed.ex	New signed-authorization struct with RLP conversion and authority recovery.
lib/ethers/authorization.ex	New authorization struct with validation and EIP-7702 hash computation.
lib/ethers.ex	Adds public sign_authorization/2 and sign_authorization!/2 helpers.
CHANGELOG.md	Notes the new EIP-7702 support in Unreleased enhancements.

Comments suppressed due to low confidence (2)

lib/ethers/transaction.ex:456

• from_rpc_authorization_list/1 parses r/s via hex_to_integer!/1 and then :binary.encode_unsigned/1, which loses any leading zeros and can change the byte representation. It also crashes if r/s are missing (because encode_unsigned(nil) raises). Using the existing from_map_value_bin/2 keeps r/s as raw bytes (consistent with how transaction r/s are decoded at lines 282–283) and avoids the nil crash.

  defp from_rpc_authorization_list(authorization_list) when is_list(authorization_list) do
    Enum.map(authorization_list, fn authorization ->
      %Authorization.Signed{
        authorization: %Authorization{
          chain_id: from_map_value_int(authorization, :chainId),
          address: authorization |> from_map_value(:address) |> Utils.to_checksum_address(),
          nonce: from_map_value_int(authorization, :nonce)
        },
        signature_y_parity: from_map_value_int(authorization, :yParity),
        signature_r: authorization |> from_map_value_int(:r) |> :binary.encode_unsigned(),
        signature_s: authorization |> from_map_value_int(:s) |> :binary.encode_unsigned()
      }

lib/ethers/transaction/eip7702.ex:127

• from_rlp_list/1 decodes to as nil when empty; after guarding against empty to this can be simplified to always decode the address. This avoids propagating an impossible nil to for type-4 transactions.

         max_fee_per_gas: :binary.decode_unsigned(max_fee_per_gas),
         gas: :binary.decode_unsigned(gas),
         to: (to != "" && Utils.encode_address!(to)) || nil,
         value: :binary.decode_unsigned(value),

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