Precompile log buffer regular expressions

Compile fixed patterns during monitor and log counter initialization, pass compiled expressions to the log buffer, and reject invalid log counter patterns before watching logs.

pkg/systemlogmonitor/config.go

@@ -59,13 +59,14 @@ func (mc *MonitorConfig) ApplyDefaultConfiguration() {
 	}
 }
 
-// ValidateRules verifies whether the regular expressions in the rules are valid.
-func (mc MonitorConfig) ValidateRules() error {
-	for _, rule := range mc.Rules {
-		_, err := regexp.Compile(rule.Pattern)
+func (mc MonitorConfig) compileRules() ([]*regexp.Regexp, error) {
+	patterns := make([]*regexp.Regexp, len(mc.Rules))
+	for i, rule := range mc.Rules {
+		pattern, err := CompilePattern(rule.Pattern)
 		if err != nil {
-			return err
+			return nil, err
 		}
+		patterns[i] = pattern
 	}
-	return nil
+	return patterns, nil
 }