test: add unit tests for common modules - #562

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/setup-go@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Include file: <iconv.h> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: "config.h" not found.

Include file: <QString> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <QVariant> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <QDebug> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <QCoreApplication> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <QObject> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: <dtkcore_config.h> not found. Please note: Cppcheck does not need standard library headers to get proper results.

Include file: "stubext.h" not found.