add private constructor for BigQueryJdbcOpenTelemetry

Author: keshavdandeva

java-bigquery/google-cloud-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/BigQueryJdbcOpenTelemetry.java

@@ -23,6 +23,8 @@ public class BigQueryJdbcOpenTelemetry {
 
   static final String INSTRUMENTATION_SCOPE_NAME = "com.google.cloud.bigquery.jdbc";
 
+  private BigQueryJdbcOpenTelemetry() {}
+
   /**
    * Initializes or returns the OpenTelemetry instance based on hybrid logic. Prefer
    * customOpenTelemetry if provided; fallback to an auto-configured GCP exporter if requested.