fix: Gradle plugin metamodel wiring for every source set and the javadoc preview flag

[zantvoort]

Fixes #415

The plugin wired the metamodel processor onto the configurations literally named annotationProcessor and ksp only. Those configurations never extend each other, so entities declared in test or custom source sets silently got no metamodel. And --enable-preview covered JavaCompile, Test and JavaExec but not Javadoc, so ./gradlew javadoc failed on the Java path: javadoc embeds the javac front end, which rejects storm-java21's preview class files without the flag.

Changes

• The plugin iterates the source-set container instead of hardcoding configuration names: storm-metamodel-processor goes on every source set's annotation-processor configuration (annotationProcessor, testAnnotationProcessor, custom equivalents), and storm-metamodel-ksp on every source set's KSP configuration (ksp, kspTest, ksp<Custom>), keeping the eager-add plus afterEvaluate opt-out pattern KSP requires. The metamodel.set(false) opt-out covers all of them.
• On the Java path with javaPreview enabled, every Javadoc task gets --enable-preview plus -source 21; an explicitly configured source level is left untouched.
• The functional tests back the declared Gradle 8.5+ support with a pinned version matrix: the declared minimum (8.5) and the last of the 8.x line (8.14.3) on both language paths via withGradleVersion; the wrapper's 9.6.1 covers the current major through all other tests.

Tests

• Functional: processor wiring asserted for testAnnotationProcessor, kspTest, and a custom integration source set on both paths; javadoc options asserted present, absent on opt-out and on the Kotlin path, and non-clobbering for a user-set source level; the version matrix runs the wiring dump on Gradle 8.5 and 8.14.3. The dump reads javadoc options reflectively (JavadocOptionFile.getOptions(), same shape since before the minimum Gradle version) because addBooleanOption has no public read accessor.
• Smoke (gated, runs in CI): a Kotlin entity in src/test/kotlin generates its metamodel under build/generated/ksp/test, a Java entity in src/test/java generates through testAnnotationProcessor, and a real ./gradlew javadoc run succeeds against a source referencing st.orm.template.ORMTemplate, which failed before the fix.

Docs: the installation page's plugin table now states the per-source-set wiring and lists javadoc among the preview-flagged tasks (docs/ only, so visible at /docs/next until the next release).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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