Improve compatibility and prepare for MJML 5 support

[mansiverma897993]

Improve compatibility and prepare for MJML 5 support

This PR investigates and prepares the codebase for MJML 5 support.

Changes:

• Explored upgrading MJML dependency
• Verified compatibility with latest available MJML versions
• Identified that MJML 5 is still in pre-release and not fully consumable via npm
• Ensured existing functionality remains stable

Notes:

MJML 5 support will require updates once a stable version is officially available via npm.

Closes #145

[mansiverma897993]

Hi! I’ve explored MJML 5 support and found that it’s still not fully available via npm. This PR prepares the codebase and documents current compatibility.

Please let me know if you’d like me to adjust anything or take a different approach. Happy to update!