Consolidate ExecutionMode type and constants to enum

[jeffsmale90]

📝 Description

Previously ExecutionMode was a type, which was implemented as multiple constant literals. Now we combine those two into a single enum ExecutionMode.

🔄 What Changed?

• type ExecutionMode = {...} and const SINGLE_DEFAULT_MODE = '0x.... etc becomes enum ExecutionMode = { SINGLE_DEFAULT = '0x...' ... }
• Update all references to use enum
• Moved from /utils export to main root export

🚀 Why?

The ExecutionMode was required by a number of interfaces in the root export. This meant that a caller would have to import the function from the root export, and the ExecutionMode constants from the /utils export. Additionally, the caller may have to import the type (by name), and each of the constants (by name). Allowing the caller to import only the enum, makes calling these functions much easier.

🧪 How to Test?

Sufficient automated testing in unit tests, and e2e integration tests. Review the integration tests to see the new interface. Take special note of the imports.

⚠️ Breaking Changes

List any breaking changes:

• No breaking changes
• Breaking changes (describe below):

ExecutionMode becomes an enum and moves from @metamask/delegation-toolkit/utils to `@metamask/delegation-toolkit.

📋 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:
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📚 Additional Notes

Any additional information, concerns, or context: