Preserve @{argLine} in AddSurefireFailsafeArgLine for JaCoCo coverage

[timtebeek]

AddSurefireFailsafeArgLine now prepends Surefire's @{argLine} late property reference whenever it writes or merges a surefire/failsafe argLine, so an -javaagent injected into the argLine property by an earlier plugin (most notably the JaCoCo coverage agent from jacoco-maven-plugin:prepare-agent, but also the Mockito/ByteBuddy agent) is preserved instead of clobbered. The reference is not added when the existing argLine already references the argLine property (@{argLine} or ${argLine}), so the recipe stays idempotent and never duplicates it. Unlike ${argLine}, the @{...} form is resolved when Surefire executes rather than at POM interpolation, so it picks up the value set during the build and resolves to an empty string when unset. Tests are updated for the new prefix, plus new cases covering JaCoCo coverage preservation and no-duplication of an existing reference; the generated examples.yml is regenerated to match.