Prepare for Gradle 9 upgrade (#2985)

Refactor Gradle scripts to replace usages incompatible with Gradle 9.

PR prepared mostly with gemini-cli, with one issue (project.exec)
researched with gemini web and manually applied.

The actual upgrade to Gradle 9 will be in another PR.

Verified: none of the issues reported in build/reports/problems/problems-report.html
is related to Gradle 9.

networking/build.gradle

@@ -56,12 +56,14 @@ task testJar(type: Jar) {
   from sourceSets.test.output
 }
 
-artifacts {
-  testRuntimeOnly testJar
-}
-
 configurations {
-  testRuntimeOnly {
+  testRuntimeElements {
     canBeConsumed = true
+    canBeResolved = false
+    extendsFrom testRuntimeOnly
   }
 }
+
+artifacts {
+  add('testRuntimeElements', testJar)
+}