Add unit tests for getDeviceTypeRFC()

[Copilot]

getDeviceTypeRFC() introduced RFC-to-device-type mapping logic ("prod", "test", "unknown") with no unit test coverage. Adds tests to fwdl_interface_gtest.cpp using the existing InterfaceTestFixture and g_InterfaceMock.

New tests

• TestName_getDeviceTypeRFCReadFailure — getRFCParameter returns WDMP_FAILURE; expects "unknown"
• TestName_getDeviceTypeRFCProd — RFC value "prod", expects "prod"
• TestName_getDeviceTypeRFCTest — RFC value "test", expects "test"
• TestName_getDeviceTypeRFCUnknown — Unrecognized RFC value ("staging"), expects "unknown"

Invoke lambdas override param->value to inject specific RFC strings through the existing mock chain:

TEST_F(InterfaceTestFixture, TestName_getDeviceTypeRFCProd)
{
    char deviceType[32] = {0};
    EXPECT_CALL(*g_InterfaceMock, getRFCParameter(_, _, _)).Times(1)
        .WillOnce(Invoke([](char* /*type*/, const char* /*key*/, RFC_ParamData_t *param) {
            snprintf(param->value, sizeof(param->value), "%s", "prod");
            return 1;
        }));
    getDeviceTypeRFC(deviceType, sizeof(deviceType));
    EXPECT_STREQ(deviceType, "prod");
}

Also adds a .gitignore to prevent autotools/build artifacts from polluting future commits.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.