make startTime in native-token-stream optional

[MoMannn]

📝 Description

Make startTime optional. In case its not defined permission snap will set startTime as Date.now() to ensure the current time for user.

🔄 What Changed?

List the specific changes made:

• startTime set to optional.

🚀 Why?

Explain the motivation behind these changes:

• Snap will set startTime in case its not set.

🧪 How to Test?

Describe how to test these changes:

• Manual testing steps:

1. Use experimental permission action with startTime not set.

• Automated tests added/updated
• All existing tests pass

⚠️ Breaking Changes

List any breaking changes:

• No breaking changes

📋 Checklist

Check off completed items:

• Code follows the project's coding standards
• Self-review completed
• Documentation updated (if needed)
• Tests added/updated
• Changelog updated (if needed)
• All CI checks pass

🔗 Related Issues

Link to related issues:
MetaMask/snap-7715-permissions#110

📚 Additional Notes

/

[jeffsmale90]

LGTM!

When we release this change in the SDK, we should ensure we have an updated version of the Snaps released, and update the experimental actions to require the updated snaps to be installed.