drop binary compatibility with java 7, ensure compiles with Java 21

Author: davidmoten

pom.xml

@@ -20,7 +20,7 @@
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <scm.url>scm:git:https://github.com/davidmoten/rxjava-jdbc.git</scm.url>
-        <maven.compiler.target>1.7</maven.compiler.target>
+        <maven.compiler.target>1.8</maven.compiler.target>
         <rxjava.version>1.3.8</rxjava.version>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <checkstyle.version>3.3.1</checkstyle.version>

src/main/java/com/github/davidmoten/rx/jdbc/QuerySelect.java

@@ -136,9 +136,10 @@ public Observable<T> call(List<Parameter> params) {
      *            one set of parameters to be run with the query
      * @return
      */
+    @SuppressWarnings("unchecked")
     private <T> Observable<T> executeOnce(final List<Parameter> params,
             ResultSetMapper<? extends T> function) {
-        return QuerySelectOnSubscribe.execute(this, params, function)
+        return (Observable<T>) QuerySelectOnSubscribe.execute(this, params, function)
                 .subscribeOn(context.scheduler());
     }