feat: Complete 6 additional SDK implementations with fixes and examples

Go Async SDK (clients/go/async/):
- Fixed case-sensitive language detection bug (.R for R language)
- Created go.mod for module management
- Added comprehensive test suite
- Created 3 examples with expected output comments
- Added README with full documentation

Java Sync SDK (clients/java/sync/):
- RENAMED: Unsandbox.java -> Un.java (matches naming convention)
- Updated class name from Unsandbox to Un
- Created pom.xml for Maven build
- Added 6 examples (simple + SDK client versions)
- Created test suite with JUnit 5
- Added README with API documentation

JavaScript Async SDK (clients/javascript/async/):
- Fixed unused import
- Created package.json with ES module support
- Added 5 examples covering all async patterns
- Created 71 tests (all passing)
- Added comprehensive README

PHP Sync SDK (clients/php/sync/):
- RENAMED: Unsandbox.php -> un.php (matches naming convention)
- Created composer.json with PSR-4 autoloading
- Created phpunit.xml for testing
- Added 4 examples with expected output comments
- Created 54 tests across 4 test files
- Added README with full documentation

Ruby Sync SDK (clients/ruby/sync/):
- Created Gemfile and un.gemspec
- Created Rakefile with test task
- Updated examples to actually use the SDK
- Added 4 examples (hello_world, async_job, language_detection, snapshots)
- Created comprehensive test suite with 30+ tests
- Added README with documentation

Rust Sync SDK (clients/rust/sync/):
- Updated Cargo.toml with example declarations
- Created 4 examples (hello_world, fibonacci, multi_language, async_polling)
- Added comprehensive README with API reference
- All dependencies verified correct

All SDKs verified:
- HMAC-SHA256 authentication implemented
- 4-tier credential system (args > env > ~/.unsandbox > ./accounts.csv)
- Expected output comments for pipeline validation
- Proper error handling
- Language detection support

clients/java/sync/examples/FibonacciClient.java

@@ -0,0 +1,79 @@
+/**
+ * Fibonacci Client example for unsandbox Java SDK - Synchronous Version
+ *
+ * Demonstrates executing CPU-bound calculations through the sync SDK.
+ * Shows proper error handling and result processing.
+ *
+ * To compile:
+ *     javac -cp ../src FibonacciClient.java
+ *
+ * To run:
+ *     export UNSANDBOX_PUBLIC_KEY="your-public-key"
+ *     export UNSANDBOX_SECRET_KEY="your-secret-key"
+ *     java -cp .:../src FibonacciClient
+ *
+ * Expected output:
+ *     Calculating fibonacci(10)...
+ *     Result status: completed
+ *     Output: fib(10) = 55
+ */
+
+import java.util.Map;
+
+public class FibonacciClient {
+
+    public static void main(String[] args) {
+        // The code to execute
+        String code = """
+            def fib(n):
+                if n <= 1:
+                    return n
+                return fib(n-1) + fib(n-2)
+
+            print(f"fib(10) = {fib(10)}")
+            """;
+
+        try {
+            // Resolve credentials from environment
+            String publicKey = System.getenv("UNSANDBOX_PUBLIC_KEY");
+            String secretKey = System.getenv("UNSANDBOX_SECRET_KEY");
+
+            if (publicKey == null || publicKey.isEmpty() ||
+                secretKey == null || secretKey.isEmpty()) {
+                System.err.println("Error: UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY environment variables required");
+                System.err.println("Run with: export UNSANDBOX_PUBLIC_KEY=your-key UNSANDBOX_SECRET_KEY=your-key");
+                System.exit(1);
+            }
+
+            // Execute the code synchronously
+            System.out.println("Calculating fibonacci(10)...");
+            Map<String, Object> result = Un.executeCode("python", code, publicKey, secretKey);
+
+            // Check for errors
+            String status = (String) result.get("status");
+            if ("completed".equals(status)) {
+                System.out.println("Result status: " + status);
+                String stdout = (String) result.get("stdout");
+                if (stdout != null) {
+                    System.out.println("Output: " + stdout.trim());
+                }
+                String stderr = (String) result.get("stderr");
+                if (stderr != null && !stderr.isEmpty()) {
+                    System.out.println("Errors: " + stderr);
+                }
+            } else {
+                System.out.println("Execution failed with status: " + status);
+                System.out.println("Error: " + result.getOrDefault("error", "Unknown error"));
+                System.exit(1);
+            }
+
+        } catch (Un.CredentialsException e) {
+            System.err.println("Credentials error: " + e.getMessage());
+            System.exit(1);
+        } catch (Exception e) {
+            System.err.println("Error: " + e.getMessage());
+            e.printStackTrace();
+            System.exit(1);
+        }
+    }
+}