Title: [Java SDK] Implement async/non-blocking client for better performance
Description:
The current Java SDK only provides blocking I/O operations through IggyTcpClient and IggyHttpClient. This severely limits performance in stream processing frameworks like Apache Flink.

Current State:

// Only blocking operations available
PolledMessages messages = client.messages().pollMessages(...); // Blocks thread

Proposed Solution:

// Add async operations
CompletableFuture<PolledMessages> future = client.messages().pollMessagesAsync(...);

Impact:

• Multi x performance improvement expected (To be measured)
• Essential for External (e.g Flink) connector efficiency
• Reduces thread usage from 10-15 to 2-4 per task

Implementation Suggestions:

• Use Netty for non-blocking I/O
• Provide CompletableFuture-based API
• Maintain backward compatibility with blocking client