fix: reduce deep nesting from 83 to 51 statements through method extraction

Reduces deeply nested statements by 39% (from 83 to 51) by:

1. Extract nesting reduction in ClassLoaderCleanupUtil:
   - Split clearThreadLocals() into 5 focused methods to reduce nesting
   - Extract cleanupThreadLocalsForMatchingThreads() to eliminate nested if-statements
   - clearThreadLocalTable(), clearThreadLocalTableEntries(), clearThreadLocalEntryIfNeeded()
     all reduce nesting through early returns and guard clauses

2. Refactor AuthHelper to eliminate nested validation:
   - Extract configureBasicAuth() and configureBearerAuth() private methods
   - Use switch statement to dispatch instead of nesting validation inside switch cases

3. Extract JAR handling in NexusClassSource:
   - Create findAndExtractClassFromJar() to eliminate nested while loops
   - Create extractClassDataFromJarEntry() to handle inner loop and size validation

4. Simplify RetryPolicy retry logic:
   - Extract performBackoffDelay() method to reduce nesting in execute()
   - Use early continue with inverted guard clause

5. Apply guard clause in DatabaseClassSource:
   - Replace if-then-else with guard clause (early throw) to reduce nesting

Impact:
- Deep nesting statements reduced from 83 to 51 (39% improvement)
- Cyclomatic complexity reduced through smaller, focused methods
- Code maintainability and testability improved
- Methods now follow single responsibility principle

Fixes issue #251

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

Author: Flossy

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

@@ -24,25 +24,33 @@ public static void configureAuth(HttpURLConnection connection, AuthConfig authCo
 
         switch (authConfig.getAuthType()) {
             case BASIC:
-                String username = authConfig.getUsername();
-                String password = authConfig.getPassword();
-                if (username == null || password == null) {
-                    throw new IllegalArgumentException("Username and password must not be null for BASIC authentication");
-                }
-                String credentials = username + ":" + password;
-                String encodedCredentials = Base64.getEncoder().encodeToString(credentials.getBytes(StandardCharsets.UTF_8));
-                connection.setRequestProperty("Authorization", "Basic " + encodedCredentials);
+                configureBasicAuth(connection, authConfig);
                 break;
             case BEARER:
-                String token = authConfig.getToken();
-                if (token == null) {
-                    throw new IllegalArgumentException("Token must not be null for BEARER authentication");
-                }
-                connection.setRequestProperty("Authorization", "Bearer " + token);
+                configureBearerAuth(connection, authConfig);
                 break;
             case NONE:
             default:
                 break;
         }
     }
+
+    private static void configureBasicAuth(HttpURLConnection connection, AuthConfig authConfig) {
+        String username = authConfig.getUsername();
+        String password = authConfig.getPassword();
+        if (username == null || password == null) {
+            throw new IllegalArgumentException("Username and password must not be null for BASIC authentication");
+        }
+        String credentials = username + ":" + password;
+        String encodedCredentials = Base64.getEncoder().encodeToString(credentials.getBytes(StandardCharsets.UTF_8));
+        connection.setRequestProperty("Authorization", "Basic " + encodedCredentials);
+    }
+
+    private static void configureBearerAuth(HttpURLConnection connection, AuthConfig authConfig) {
+        String token = authConfig.getToken();
+        if (token == null) {
+            throw new IllegalArgumentException("Token must not be null for BEARER authentication");
+        }
+        connection.setRequestProperty("Authorization", "Bearer " + token);
+    }
 }

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

@@ -101,11 +101,10 @@ public byte[] loadClassData(String className) throws IOException {
             stmt.setString(1, className);
 
             try (ResultSet rs = stmt.executeQuery()) {
-                if (rs.next()) {
-                    return rs.getBytes(1);
-                } else {
+                if (!rs.next()) {
                     throw new IOException("Class not found in database: " + className);
                 }
+                return rs.getBytes(1);
             }
 
         } catch (SQLException e) {