Build system: remove gtest/gmock from the project and restore unit test build/run coverage

[johnny9]

Summary

Remove gtest/gmock from the gui-qml project and make sure unit test build/run coverage still works afterward.

Why

Issue #753 is currently blocked on undoing the gtest/gmock work. We should track that removal explicitly as build-system work.

Scope

• Remove gtest/gmock from the project and related build wiring
• Restore or replace the affected unit test build/run flow
• Update CI/build scripts as needed so test coverage still runs in a supported way

Related

• Blocks Enable tests in depends workflow when we undo gtest/gmock #753