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/controller/web/AccountWebController.java

@@ -123,9 +123,7 @@ public class AccountWebController {
             String saml2AuthenticationPath = "/saml2/authenticate/" + saml2.getRegistrationId();
 
             if (applicationProperties.getEnterpriseEdition().isSsoAutoLogin()) {
-                return "redirect:"
-                        + request.getRequestURL()
-                        + saml2AuthenticationPath;
+                return "redirect:" + request.getRequestURL() + saml2AuthenticationPath;
             } else {
                 providerList.put(saml2AuthenticationPath, samlIdp + " (SAML 2)");
             }
@@ -329,21 +327,21 @@ public class AccountWebController {
         if (authentication == null || !authentication.isAuthenticated()) {
             return "redirect:/";
         }
-        if (authentication != null && authentication.isAuthenticated()) {
+        if (authentication.isAuthenticated()) {
             Object principal = authentication.getPrincipal();
             String username = null;
 
             // Retrieve username and other attributes and add login attributes to the model
-            if (principal instanceof UserDetails userDetails) {
-                username = userDetails.getUsername();
+            if (principal instanceof UserDetails detailsUser) {
+                username = detailsUser.getUsername();
                 model.addAttribute("oAuth2Login", false);
             }
-            if (principal instanceof OAuth2User userDetails) {
-                username = userDetails.getName();
+            if (principal instanceof OAuth2User oAuth2User) {
+                username = oAuth2User.getName();
                 model.addAttribute("oAuth2Login", true);
             }
-            if (principal instanceof CustomSaml2AuthenticatedPrincipal userDetails) {
-                username = userDetails.name();
+            if (principal instanceof CustomSaml2AuthenticatedPrincipal saml2User) {
+                username = saml2User.name();
                 model.addAttribute("saml2Login", true);
             }
             if (username != null) {
@@ -395,10 +393,10 @@ public class AccountWebController {
         if (authentication == null || !authentication.isAuthenticated()) {
             return "redirect:/";
         }
-        if (authentication != null && authentication.isAuthenticated()) {
+        if (authentication.isAuthenticated()) {
             Object principal = authentication.getPrincipal();
-            if (principal instanceof UserDetails userDetails) {
-                String username = userDetails.getUsername();
+            if (principal instanceof UserDetails detailsUser) {
+                String username = detailsUser.getUsername();
                 // Fetch user details from the database
                 Optional<User> user = userRepository.findByUsernameIgnoreCase(username);
                 if (user.isEmpty()) {