Improve Type-Safe Casting with Pattern Matching (#2990)

# Description of Changes

Please provide a summary of the changes, including:

This PR refactors multiple instances of type casting throughout the
codebase by replacing them with Java's pattern matching for
`instanceof`. This approach eliminates redundant type casting, improves
code readability, and reduces the chances of `ClassCastException`. The
changes primarily affect authentication handling, PDF processing, and
certificate validation.

### Key Changes:
- Replaced traditional `instanceof` checks followed by explicit casting
with pattern matching.
- Improved readability and maintainability of type-related operations.
- Applied changes across security modules, PDF utilities, and image
processing functions.

This refactor does not introduce new functionality but enhances the
robustness and clarity of the existing code.

pending until #2818 is published

---

## Checklist

### General

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

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#6-testing)
for more details.

src/main/java/stirling/software/SPDF/config/security/saml2/CertificateUtils.java

@@ -40,13 +40,12 @@ public class CertificateUtils {
             Object object = pemParser.readObject();
             JcaPEMKeyConverter converter = new JcaPEMKeyConverter();
 
-            if (object instanceof PEMKeyPair) {
+            if (object instanceof PEMKeyPair keypair) {
                 // Handle traditional RSA private key format
-                PEMKeyPair keypair = (PEMKeyPair) object;
                 return (RSAPrivateKey) converter.getPrivateKey(keypair.getPrivateKeyInfo());
-            } else if (object instanceof PrivateKeyInfo) {
+            } else if (object instanceof PrivateKeyInfo keyInfo) {
                 // Handle PKCS#8 format
-                return (RSAPrivateKey) converter.getPrivateKey((PrivateKeyInfo) object);
+                return (RSAPrivateKey) converter.getPrivateKey(keyInfo);
             } else {
                 throw new IllegalArgumentException(
                         "Unsupported key format: "

src/main/java/stirling/software/SPDF/config/security/saml2/CustomSaml2AuthenticatedPrincipal.java

@@ -8,7 +8,11 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.security.saml2.provider.service.authentication.Saml2AuthenticatedPrincipal;
 
 @ConditionalOnProperty(name = "security.saml2.enabled", havingValue = "true")
-public record CustomSaml2AuthenticatedPrincipal(String name, Map<String, List<Object>> attributes, String nameId, List<String> sessionIndexes)
+public record CustomSaml2AuthenticatedPrincipal(
+        String name,
+        Map<String, List<Object>> attributes,
+        String nameId,
+        List<String> sessionIndexes)
         implements Saml2AuthenticatedPrincipal, Serializable {
 
     @Override
@@ -20,5 +24,4 @@ public record CustomSaml2AuthenticatedPrincipal(String name, Map<String, List<Ob
     public Map<String, List<Object>> getAttributes() {
         return this.attributes;
     }
-
 }

src/main/java/stirling/software/SPDF/config/security/saml2/CustomSaml2AuthenticationSuccessHandler.java

@@ -41,8 +41,8 @@ public class CustomSaml2AuthenticationSuccessHandler
         Object principal = authentication.getPrincipal();
         log.debug("Starting SAML2 authentication success handling");
 
-        if (principal instanceof CustomSaml2AuthenticatedPrincipal) {
-            String username = ((CustomSaml2AuthenticatedPrincipal) principal).name();
+        if (principal instanceof CustomSaml2AuthenticatedPrincipal saml2Principal) {
+            String username = saml2Principal.name();
             log.debug("Authenticated principal found for user: {}", username);
 
             HttpSession session = request.getSession(false);