Testing Neodynamic ZPL to PNG conversion

Replace license information in the placeholders:

private const string licenseOwner = "CHANGE ME";
private const string licenseKey = "CHANGE ME";

Run the tests in Docker container:

docker build -t zpl2png-test .

Run the tests locally:

dotnet test ZplRenderingTests

When running tests locally, the resulting label PNGs are generated in the build output directory.