chore: clean up MITM logs and add Google SSE tests

- Demote non-LLM request logs to debug (only streamGenerateContent at info)
- Demote non-streaming response headers to debug
- Add 5 Google SSE parser tests (single event, multi-event accumulation,
  chunked framing, completion detection, no-thinking-tokens)
- Fix unused variable warning in proxy.rs

src/mitm/proxy.rs

@@ -512,7 +512,7 @@ async fn handle_http_over_tls(
         }
 
         // Parse the HTTP request to find headers and body
-        let (headers_end, content_length, is_streaming_request) = parse_http_request_meta(&request_buf);
+        let (headers_end, content_length, _is_streaming_request) = parse_http_request_meta(&request_buf);
 
         // Try to extract cascade hint from request body
         let cascade_hint = if headers_end < request_buf.len() {
@@ -533,14 +533,22 @@ async fn handle_http_over_tls(
             }
         };
 
-        info!(
-            domain,
-            req_path = %req_path,
-            content_length,
-            streaming = is_streaming_request,
-            cascade = ?cascade_hint,
-            "MITM: forwarding request"
-        );
+        // Log LLM calls at info, everything else at debug
+        if req_path.contains("streamGenerateContent") {
+            info!(
+                domain,
+                req_path = %req_path,
+                cascade = ?cascade_hint,
+                "MITM: forwarding LLM request"
+            );
+        } else {
+            debug!(
+                domain,
+                req_path = %req_path,
+                content_length,
+                "MITM: forwarding request"
+            );
+        }
 
         // ── Ensure upstream connection is alive ──────────────────────────────
         // Lazily connect on first request, or reconnect if the previous connection died
@@ -643,10 +651,15 @@ async fn handle_http_over_tls(
                         }
                     }
 
-                    info!(domain, streaming = is_streaming_response,
-                        content_length = ?response_content_length,
-                        content_type = %content_type,
-                        status = resp.code, "MITM: got response headers");
+                    if is_streaming_response {
+                        info!(domain,
+                            content_type = %content_type,
+                            status = resp.code, "MITM: streaming response");
+                    } else {
+                        debug!(domain,
+                            content_type = %content_type,
+                            status = resp.code, "MITM: response headers");
+                    }
                     headers_parsed = true;
 
                     // Save body for usage parsing