refactor(api): replace regex string literals with Pattern instances for improved performance and readability (#5680)

# Description of Changes

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## Checklist

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- [ ] I have read the [Contribution
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- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
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Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
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- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

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### Testing (if applicable)

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---------

Signed-off-by: Balázs Szücs <[email protected]>

app/proprietary/src/test/java/stirling/software/proprietary/security/service/TotpServiceTest.java

@@ -8,6 +8,7 @@ import static org.junit.jupiter.api.Assertions.assertTrue;
 import java.lang.reflect.Method;
 import java.nio.charset.StandardCharsets;
 import java.time.Instant;
+import java.util.regex.Pattern;
 
 import org.junit.jupiter.api.Test;
 
@@ -16,6 +17,8 @@ import stirling.software.proprietary.security.util.Base32Codec;
 
 class TotpServiceTest {
 
+    private static final Pattern PATTERN = Pattern.compile("[A-Z2-7]+");
+
     private TotpService buildService(String appName) {
         ApplicationProperties properties = new ApplicationProperties();
         ApplicationProperties.Ui ui = new ApplicationProperties.Ui();
@@ -32,7 +35,7 @@ class TotpServiceTest {
 
         assertNotNull(secret);
         assertEquals(32, secret.length());
-        assertTrue(secret.matches("[A-Z2-7]+"));
+        assertTrue(PATTERN.matcher(secret).matches());
     }
 
     @Test