Sdk 5178 upgrade to jakarta servlet

[tanya732]

1. Java & Servlet API Upgrade

Migrated from javax.servlet to jakarta.servlet:

1. All imports referencing javax.servlet have been updated to jakarta.servlet.
2. This affects core classes, test classes, and all Javadoc references.

2. Gradle Upgrade

1. Gradle Wrapper updated:
2. Upgraded Gradle from 6.9.2 to 8.7.
3. Updated related wrapper scripts (gradlew, gradlew.bat, and gradle-wrapper.properties) to match new Gradle conventions and improve error handling/messaging.
4. Improved cross-platform compatibility and script robustness.

Migrate to Java 11+, Jakarta Servlet 5+, and Modernize Build
What & Why
Java & Servlet API Migration:
Migrates the codebase from Java 8 and javax.servlet (Servlet 3) to Java 11+ and jakarta.servlet (Servlet 5+), in line with the modern Jakarta EE ecosystem. This future-proofs the library and enables compatibility with current servlet containers.
Gradle Build Modernization:
Upgrades the Gradle wrapper and scripts to version 8.7, bringing in enhanced build performance, security fixes, and improved cross-platform support.

Key Changes

Source & Test Code:
Updates all imports from javax.servlet.* to jakarta.servlet.*.
Updates Javadoc references accordingly.
Gradle Wrapper:
Bumps to Gradle 8.7, updates scripts for improved error handling and POSIX compliance.
Tests:
Uses matchesPattern in assertions for cookie headers to handle new attributes (like Expires).

Impact
Breaking Change:
Users must use Java 11 or higher and a servlet container supporting Jakarta Servlet 5+.
Build:
Build scripts are now aligned with current Gradle best practices.
Tests:
More robust tests, less prone to breakage from minor header formatting changes.

🙏 Credits
Inspired by the foundational work done in #156 — big thanks to TareqK for leading this migration effort.