fix: lazy load @react-email/render to avoid Edge Runtime warnings in …

[mzubair481]

Fix Edge Runtime Warning Due to Unconditional @react-email/render Import

Note: This is a resubmission of #466 with the same changes, as the previous PR couldn't be reopened.
Note: This is just a workaround to avoid the edge runtime issues and only works for text based emails

Description

This PR fixes the Edge Runtime warning that occurs in Next.js 15 projects when using the Resend SDK, even when not using React components for emails. The warning was caused by unconditional importing of @react-email/render.

Changes

• Moved React email rendering logic to a separate render.ts file
• Implemented lazy loading of @react-email/render only when needed
• Added proper type safety and error handling
• Improved Edge Runtime compatibility
• Maintained backward compatibility

Testing

• Added tests for React email rendering functionality
• Verified Edge Runtime compatibility in Next.js 15
• Tested backward compatibility with existing code
• All existing tests passing

Breaking Changes

None. This is a backward-compatible improvement that only affects the internal implementation.

Related Issues

#467