Add native Rust WebSocket client for Switchboard Surge

[didobagi]

Summary

Adds a native Rust WebSocket client for Switchboard Surge real-time price feeds as an optional feature.

Changes

New surge feature providing:

• WebSocket client with builder pattern API
• Real-time price streaming via bundle-based subscriptions
• Automatic reconnection with exponential backoff
• Support for oracle and crossbar subscription modes
• Proper bundle ID tracking for unsubscribe operations

Implementation details:

• New src/surge/ module with client, protocol, connection handling, and configuration
• Three usage examples: quickstart, subscription management, error handling
• 49 unit tests covering protocol and connection logic

Testing

All tests pass with and without the surge feature enabled:

• cargo test --features surge - 49 tests
• cargo test - 9 base SDK tests
• cargo test --all-features - 58 total tests

Verified against production Surge gateway.

Dependencies

Added thiserror to base dependencies and tokio-tungstenite as optional dependency. The surge feature reuses existing optional dependencies (tokio, futures, reqwest, serde_json).

Compatibility

Fully backward compatible. The surge feature is opt-in and doesn't modify existing SDK functionality. Integrates with the 0.10.0 Cargo.toml structure supporting both Solana v2 and v3.