test: check request errors and stop asserting PathRewrite on /v1/models

/v1/models is served from config by ServeHTTP (task 2.5) so it never reaches
routing; the rewrite test now uses a non-reserved path.

internal/proxy/timeout_test.go

@@ -102,7 +102,10 @@ func TestReadTimeout(t *testing.T) {
 	defer server.Close()
 
 	start := time.Now()
-	resp, _ := http.Get(server.URL + "/test")
+	resp, err := http.Get(server.URL + "/test")
+	if err != nil {
+		t.Fatalf("request failed: %v", err)
+	}
 	elapsed := time.Since(start)
 
 	// Should timeout around the read timeout (with some tolerance)