test: warm up g++ before judging to avoid cold-start penalty

First g++ invocation on CI takes ~45s (cold start). Subsequent
invocations take ~300ms. Pre-compile a trivial program in initTestCase()
so the judging test only sees the warm-cache timing.

Author: ZnPdCo

tests/test1/main.cpp

@@ -159,6 +159,20 @@ class TestContest : public QObject {
 			}
 		};
 		copyDir(m_contestDir, dst, copyDir);
+
+		// Warm up g++: compile a trivial program to pay the cold-start cost
+		// upfront instead of during the timed judging test.
+		{
+			QString gppPath = QStandardPaths::findExecutable("g++");
+			if (!gppPath.isEmpty()) {
+				QProcess warmup;
+				warmup.start(gppPath, {"-x", "c++", "-O2", "-o",
+				              m_tempWorkDir.path() + "/_warmup.exe", "-"});
+				warmup.write("int main(){return 0;}");
+				warmup.closeWriteChannel();
+				warmup.waitForFinished(60000);
+			}
+		}
 	}
 
 	// ------------------------------------------------------------------