fix: clear perArtifactLocks map in close() to prevent memory leak

Resolves #364 - perArtifactLocks map now cleared along with other caches
to prevent unbounded growth from accumulated lock objects.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: Flossy

src/main/java/org/flossware/classloader/MavenRepositoryClassSource.java

@@ -416,6 +416,7 @@ public void close() throws IOException {
                 }
             }
             jarPathCache.clear();
+            perArtifactLocks.clear();
 
             // Throw aggregated exception if any occurred
             if (!exceptions.isEmpty()) {