fix: use maven-metadata.xml to look up the latest test framework version

The previous implementation queried search.maven.org's Solr endpoint and
returned the `latestVersion` field. That index has been frozen since
around May 2025 (a side effect of the Sonatype migration to
central.sonatype.com), so the endpoint now serves stale data. For
example, the latest version it reports for
`junit-platform-console-standalone` is `1.13.0-M3` (a JUnit 5 milestone),
while the actual current stable on Maven Central is `6.1.0`. As a
result, `Enable Java Tests` ends up downloading either that milestone
or, after falling back, the hard-coded `1.9.3`.

Switch the lookup to the artifact's own `maven-metadata.xml` on
repo1.maven.org, which is the authoritative metadata maintained
alongside the artifact:

* Prefer the `<release>` tag (Maven's pointer to the latest non-snapshot
  version).
* Fall back to scanning `<version>` entries from newest to oldest for
  the first stable build.
* Pre-release qualifiers (`-M*`, `-RC*`, `-beta`, `-SNAPSHOT`, etc.) are
  rejected via `isStableVersion`.

Also bump the JUnit Jupiter `defaultVersion` from `1.9.3` to `6.1.0` so
the offline fallback matches a currently published stable.

Related to #1866

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: wenytang-ms

src/commands/testDependenciesCommands.ts

@@ -138,7 +138,7 @@ function getJarIds(testKind: TestKind): IArtifactMetadata[] {
             return [{
                 groupId: 'org.junit.platform',
                 artifactId: 'junit-platform-console-standalone',
-                defaultVersion: '1.9.3',
+                defaultVersion: '6.1.0',
             }];
         case TestKind.JUnit:
             return [{
@@ -172,20 +172,43 @@ function getJarIds(testKind: TestKind): IArtifactMetadata[] {
 
 async function getLatestVersion(groupId: string, artifactId: string): Promise<string | undefined> {
     try {
-        const response: any = await getHttpsAsJSON(getQueryLink(groupId, artifactId));
+        const xml: string = await getHttpsAsText(getMetadataLink(groupId, artifactId));
 
-        if (!response.response?.docs?.[0]?.latestVersion) {
-            sendError(new Error('Invalid format for the latest version response'));
-            return undefined;
+        // Prefer the <release> tag (Maven's authoritative pointer to the latest non-snapshot version).
+        const releaseMatch: RegExpMatchArray | null = xml.match(/<release>([^<]+)<\/release>/);
+        if (releaseMatch && isStableVersion(releaseMatch[1])) {
+            return releaseMatch[1];
         }
-        return response.response.docs[0].latestVersion;
+
+        // Fallback: scan <version> entries (chronologically ordered) for the newest stable version,
+        // in case <release> is missing or points to a milestone / RC.
+        const versionRegex: RegExp = /<version>([^<]+)<\/version>/g;
+        const versions: string[] = [];
+        let match: RegExpExecArray | null;
+        while ((match = versionRegex.exec(xml)) !== null) {
+            versions.push(match[1]);
+        }
+        for (let i: number = versions.length - 1; i >= 0; i--) {
+            if (isStableVersion(versions[i])) {
+                return versions[i];
+            }
+        }
+
+        sendError(new Error(`No stable version found in maven-metadata.xml for ${groupId}:${artifactId}`));
     } catch (e) {
         sendError(new Error(`Failed to fetch the latest version for ${groupId}:${artifactId}`));
     }
 
     return undefined;
 }
 
+function isStableVersion(version: string): boolean {
+    // A stable Maven version is composed solely of dot-separated numeric segments
+    // (e.g. 6.1.0, 4.13.2). Anything with a qualifier such as -M3, -RC1, -beta-1
+    // or -SNAPSHOT is treated as a pre-release.
+    return /^\d+(\.\d+)*$/.test(version);
+}
+
 async function downloadJar(
     libFolder: string,
     groupId: string,
@@ -274,9 +297,9 @@ async function updateProjectSettings(projectUri: Uri, libFolder: string): Promis
     window.showInformationMessage(`Test libraries have been downloaded into '${relativePath}/'.`);
 }
 
-async function getHttpsAsJSON(link: string): Promise<any> {
+async function getHttpsAsText(link: string): Promise<string> {
     // eslint-disable-next-line @typescript-eslint/typedef
-    const response: string = await new Promise<string>((resolve, reject) => {
+    return new Promise<string>((resolve, reject) => {
         let result: string = '';
         https.get(link, {
             headers: {
@@ -295,7 +318,6 @@ async function getHttpsAsJSON(link: string): Promise<any> {
             res.on('error', reject);
         });
     });
-    return JSON.parse(response);
 }
 
 async function getTotalBytes(url: string): Promise<number> {
@@ -315,8 +337,8 @@ async function getTotalBytes(url: string): Promise<number> {
     });
 }
 
-function getQueryLink(groupId: string, artifactId: string): string {
-    return `https://search.maven.org/solrsearch/select?q=id:%22${groupId}:${artifactId}%22&rows=1&wt=json`;
+function getMetadataLink(groupId: string, artifactId: string): string {
+    return `https://repo1.maven.org/maven2/${groupId.split('.').join('/')}/${artifactId}/maven-metadata.xml`;
 }
 
 function getDownloadLink(groupId: string, artifactId: string, version: string): string {