fix: support implicit `@MethodSource` to `UnusedMethod`

[JarvisCraft]

Currently, UnusedMethod check does not recognize implicitly referenced JUnit @MethodSource, e.g. the ones which are derived from test method name when none are specified explicitly. This PR fixes this issue.

Fixes #5289

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[JarvisCraft]

Hi @cushon, @graememorgan; could you please run the CI on this PR?

[Pankraz76]

nice plz include @After also this is kind of a general topic having to watch many actually all? junit annotations.

There will be new stuff to come for sure.

right @marcphilipp?

thank you.

• https://github.com/opensearch-project/OpenSearch/pull/19896
• https://github.com/opensearch-project/OpenSearch/blob/46164b5b678d3be68d04446d186ae429c7544d13/test/framework/src/main/java/org/opensearch/search/aggregations/AggregatorTestCase.java#L1369
• https://github.com/opensearch-project/OpenSearch/actions/runs/19101079871/job/54572915387?pr=19896

/home/runner/work/OpenSearch/OpenSearch/test/framework/src/main/java/org/opensearch/search/aggregations/AggregatorTestCase.java:1370: error: [UnusedMethod] Method 'cleanupReleasables' is never used.
    private void cleanupReleasables() {

[marcphilipp]

@Pankraz76 @After is from JUnit 4 and such methods must be public.