fix(core): normalize rule keywords and optimize base64 decoding

Author: TheArqsz

src/main/java/com/arqsz/burpgitleaks/config/RuleLoader.java

@@ -164,7 +164,9 @@ private static GitleaksRule parseRule(TomlTable t, String id, String sourceName)
         String regex = t.getString("regex");
         String path = t.getString("path");
 
-        List<String> keywords = toList(t.getArray("keywords"));
+        List<String> keywords = toList(t.getArray("keywords")).stream()
+                .map(String::toLowerCase)
+                .toList();
 
         List<GitleaksAllowlist> localAllowlists = extractAllowlists(t, "Rule Allowlist (" + id + ")");
 

src/main/java/com/arqsz/burpgitleaks/scan/GitleaksScanCheck.java

@@ -357,12 +357,20 @@ private String tryDecode(String s) {
     }
 
     private boolean isPrintable(String s) {
-        if (s.isEmpty())
+        if (s == null || s.isEmpty())
             return false;
-        long controlChars = s.chars()
-                .filter(c -> (c < 32 && c != '\n' && c != '\r' && c != '\t') || c > 126)
-                .count();
-        return (double) controlChars / s.length() < 0.3;
+
+        int controlChars = 0;
+        int len = s.length();
+
+        for (int i = 0; i < len; i++) {
+            char c = s.charAt(i);
+            if ((c < 32 && c != '\n' && c != '\r' && c != '\t') || c > 126) {
+                controlChars++;
+            }
+        }
+
+        return (double) controlChars / len < 0.3;
     }
 
     private String extractLine(String body, int start, int end) {