Improve Vert.x SQL stable metric tests

[trask]

Summary

• use the shared DB duration metric helper in the Vert.x SQL 4.0 and 5.0 stable semconv tests
• assert the stable metric unit, description, histogram points, and expected attribute keys instead of checking only the metric name

[Copilot]

Pull request overview

This PR strengthens the Vert.x SQL client stable semantic convention (stable semconv) metric tests by switching to the shared DB client duration metric assertion helper and validating metric metadata and attribute keys (not just metric name).

Changes:

• Replace ad-hoc waitAndAssertMetrics(... hasName("db.client.operation.duration")) checks with DbClientMetricsTestUtil.assertDurationMetric(...).
• Assert stable metric unit (s), description, histogram structure, and that histogram point attributes contain only the expected semantic convention keys.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
instrumentation/vertx/vertx-sql-client/vertx-sql-client-5.0/javaagent/src/test/java/io/opentelemetry/javaagent/instrumentation/vertx/sqlclient/v5_0/VertxSqlClientTest.java	Use shared duration-metric helper and assert expected stable metric metadata + attribute keys.
instrumentation/vertx/vertx-sql-client/vertx-sql-client-4.0/javaagent/src/test/java/io/opentelemetry/javaagent/instrumentation/vertx/sqlclient/v4_0/VertxSqlClientTest.java	Use shared duration-metric helper and assert expected stable metric metadata + attribute keys.