Monitor for faulty CodeGenerators and ProgramTemplates

This change adds some logic to periodically (currently every 5 minutes)
check for CodeGenerators and ProgramTemplates that have a very low
correctness rate, which might indicate that they are not working correctly.

Sources/Fuzzilli/Fuzzer.swift

@@ -262,6 +262,20 @@ public class Fuzzer {
             }
         }
 
+        // Install a timer to monitor for faulty code generators and program templates.
+        timers.scheduleTask(every: 5 * Minutes) {
+            for generator in self.codeGenerators {
+                if generator.totalSamples >= 100 && generator.correctnessRate < 0.05 {
+                    self.logger.warning("Code generator \(generator.name) might be broken. Correctness rate is only \(generator.correctnessRate * 100)% after \(generator.totalSamples) generated samples")
+                }
+            }
+            for template in self.programTemplates {
+                if template.totalSamples >= 100 && template.correctnessRate < 0.05 {
+                    self.logger.warning("Program template \(template.name) might be broken. Correctness rate is only \(template.correctnessRate * 100)% after \(template.totalSamples) generated samples")
+                }
+            }
+        }
+
         // Determine our initial state if necessary.
         assert(state == .uninitialized || state == .corpusImport)
         if state == .uninitialized {