[Java SDK] Add AutoCloseable support and proper cleanup

**Title:** `[Java SDK] Add AutoCloseable support and proper cleanup`

**Description:**
Current clients don't implement AutoCloseable and lack proper cleanup methods.

**Proposed Solution:**
```java
public interface IggyClient extends AutoCloseable {
void connect() throws IggyException;
void close() throws IggyException;
boolean isConnected();

// Health check
CompletableFuture healthCheck();
}

// Usage with try-with-resources
try (IggyClient client = IggyClient.builder().build()) {
// Use client
} // Automatic cleanup
```