Enhance TLS Emulator with ALPN Support and Add Adversarial Tests

- Modified `build_emulated_server_hello` to accept ALPN (Application-Layer Protocol Negotiation) as an optional parameter, allowing for the embedding of ALPN markers in the application data payload.
- Implemented logic to handle oversized ALPN values and ensure they do not interfere with the application data payload.
- Added new security tests in `emulator_security_tests.rs` to validate the behavior of the ALPN embedding, including scenarios for oversized ALPN and preference for certificate payloads over ALPN markers.
- Introduced `send_adversarial_tests.rs` to cover edge cases and potential issues in the middle proxy's send functionality, ensuring robustness against various failure modes.
- Updated `middle_proxy` module to include new test modules and ensure proper handling of writer commands during data transmission.

src/transport/middle_proxy/pool.rs

@@ -692,6 +692,7 @@ impl MePool {
         }
     }
 
+    #[allow(dead_code)]
     pub(super) fn draining_active_runtime(&self) -> u64 {
         self.draining_active_runtime.load(Ordering::Relaxed)
     }