fix: raise errors instead of returning fake data when C++ extension is unavailable

[vtz]

Summary

• RPC, Transport, Events: Operations that require the native C++ extension (RpcClient.call(), Transport.send(), EventSubscriber.subscribe(), EventPublisher.notify(), EventPublisher.set_field()) now raise clear errors (RpcError, TransportError, RuntimeError) instead of silently returning empty/fake responses or dropping messages.
• Error propagation: RpcClient.call() now wraps native C++ exceptions in RpcError and raises on non-zero result codes, instead of swallowing errors with except Exception: pass.
• README: Added "Verify native extension" subsection after Installation and updated the troubleshooting section to describe the new error-raising behavior.

Test plan

• pytest tests/unit/ — 271 tests pass
• pytest tests/ — all 300 tests pass (unit + integration + property)
• Tests updated to assert RpcError / TransportError / RuntimeError when C++ extension is unavailable
• New tests: test_call_raises_without_native, test_call_propagates_cpp_exception, test_call_async_raises_without_native, test_send_raises_without_native, test_subscribe_raises_without_native, test_notify_raises_without_native, test_set_field_raises_without_native
• Verify on macOS without C++ extension: import opensomeip succeeds, client.call(...) raises RpcError with helpful message

Fixes #17

Made with Cursor