Run the README check and the scale test as test suite targets - #28

Summary

The README check gets its own task. The correlator's test task declared README.md as an input, because CommandLineTest.readmeMatchesParser checks the README's option tables against the CLI parser. Any README edit therefore reran the whole correlator unit suite, about 50 seconds per CI job. That includes the release workflow's version update: see the v0.6.0 README update run.

• readmeMatchesParser carries the readme tag, and test excludes it.
• A new readmeTest task runs only that test. It is the only task whose input is the README, and check depends on it.

Extra test tasks are suite targets. Following the Gradle 9 upgrade guide's recommendation for adding extra Test tasks:

• readmeTest is registered as a target of the test suite.
• scaleTest is registered as a target of the integrationTest suite, where it used to be a plain Test task with testClassesDirs and classpath wired by hand.
• Both get their suite's classes, runtime classpath and test framework, plus anything the build configures on every target. Each keeps only its tag filter and its own settings.

The correlator JAR leaves the integrationTest classpath. It was there for the public API check, which now runs in packagedJarTest with the JAR on its own classpath, and for the removed compatibility JFR test. No remaining integration test uses it. The agent's classpath += files(agentJar) stays: its host-native tests load the native bundle from the JAR's META-INF/native resources.

check depends on the suites. Following the JVM Test Suite plugin guide, check now depends on the test and integrationTest suites instead of their default tasks, so every target of a suite runs with it. That makes the hand-written dependencies on readmeTest and scaleTest unnecessary. A dry run shows each module's check running the same test tasks as before.

packagedJarTest stays a plain Test task. Its classpath is deliberately the shaded JAR and the bare test libraries, without the suite's runtime classpath. The agent's containerIntegrationTest… tasks are a custom task type, not Test.

Verification

• ./gradlew spotlessCheck :jonoffcpu-agent:check :jonoffcpu-correlator:check :jonoffcpu-jfr-converter:check passes. With --configuration-cache-problems=warn it reports no problems, and the second run reuses the configuration cache.
• readmeTest runs exactly readmeMatchesParser, and scaleTest runs exactly retentionTracksDistinctStacksNotIntervals.
• After a temporary README edit, :jonoffcpu-correlator:test, integrationTest and scaleTest stayed UP-TO-DATE. Only readmeTest reran, or came from the cache.