feat(api): add streaming support and fix test isolation

- Add AnthropicStreamingRequest with stream: true for SSE
- Implement parse_sse_stream for real-time response parsing
- Extract do_send_with_retry as generic retry function
- Fix test parallel race conditions with #[serial]
- Add SSE event parsing unit tests
- Remove broken providers_test_generated.rs
- Add futures dependency for StreamExt
- Fix Metric/ChannelConfig import errors

Author: Developer

Cargo.toml

@@ -67,7 +67,9 @@ clap = { version = "4", features = ["derive"] }
 rand = "0.8"
 
 # HTTP client for WhatsApp MCP
-reqwest = { version = "0.12", features = ["json"] }
+reqwest = { version = "0.12", features = ["json", "stream"] }
+
+futures = "0.3"
 
 # Web server for Telegram webhook
 axum = { version = "0.7", features = ["json"] }