Account for non-test transitive dependency scopes

[wilx]

Summary

Avoid recommending test scope for a direct dependency when the same artifact
is still required transitively on the compile or runtime dependency graph.

The analyzer now builds separate compile and runtime graphs without the direct
test-only candidates and suppresses the warning for candidates that remain
reachable. This prevents an unsafe scope change: Maven conflict mediation can
otherwise hide the required transitive artifact behind the direct test-scoped
declaration.

Fixes #295

Validation

• Maven 3.9.16 / JDK 21: mvn -Prun-its verify
• Maven 4 / JDK 21: mvn clean -Prun-its verify
• Maven 3.9.16 / JDK 8: 128 unit tests passed
• Maven Dependency Plugin downstream check: 415 unit tests passed; 102 of 103
  Invoker projects passed. The remaining project asserts the previous scope
  recommendation and passes with the unpatched analyzer. Its dependency graph
  contains the exact condition fixed here: JUnit is also reachable through
  maven-project -> plexus-container-default.

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