Added a ragger ethereum client with EIP712 support

tests/ragger/conftest.py

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+import pytest
+from ragger import Firmware
+from ragger.backend import SpeculosBackend, LedgerCommBackend, LedgerWalletBackend, BackendInterface
+from ethereum_client import EthereumClient
+
+# This variable is needed for Speculos only (physical tests need the application to be already installed)
+APPLICATION = "../../bin/app.elf"
+# This variable will be useful in tests to implement different behavior depending on the firmware
+NANOX_FIRMWARE = Firmware("nanox", "2.0.2")
+NANOS_FIRMWARE = Firmware("nanos", "2.1")
+NANOSP_FIRMWARE = Firmware("nanosp", "1.0")
+
+# adding a pytest CLI option "--backend"
+def pytest_addoption(parser):
+    print(help(parser.addoption))
+    parser.addoption("--backend", action="store", default="speculos")
+
+# accessing the value of the "--backend" option as a fixture
+@pytest.fixture(scope="session")
+def backend_name(pytestconfig) -> str:
+    return pytestconfig.getoption("backend")
+
+# Providing the firmware as a fixture
+@pytest.fixture
+def firmware() -> Firmware:
+    return NANOX_FIRMWARE
+
+# Depending on the "--backend" option value, a different backend is
+# instantiated, and the tests will either run on Speculos or on a physical
+# device depending on the backend
+def create_backend(backend: str, firmware: Firmware) -> BackendInterface:
+    if backend.lower() == "ledgercomm":
+        return LedgerCommBackend(firmware, interface="hid")
+    elif backend.lower() == "ledgerwallet":
+        return LedgerWalletBackend(firmware)
+    elif backend.lower() == "speculos":
+        return SpeculosBackend(APPLICATION, firmware)
+    else:
+        raise ValueError(f"Backend '{backend}' is unknown. Valid backends are: {BACKENDS}")
+
+# This fixture will create and return the backend client
+@pytest.fixture
+def backend_client(backend_name: str, firmware: Firmware) -> BackendInterface:
+    with create_backend(backend_name, firmware) as b:
+        yield b
+
+# This final fixture will return the properly configured app client, to be used in tests
+@pytest.fixture
+def app_client(backend_client: BackendInterface) -> EthereumClient:
+    yield EthereumClient(backend_client)