chore: add #[non_exhaustive] to public enums/structs

[jamadeo]

In preparation for a 1.0 release, we should use #[non_exaustive] for most public structs/enums to help reduce backwards-incompatible changes.

It may not be appropriate in every case.

Motivation and Context

This will prevent clients from writing code that will break and require updates in future versions.

How Has This Been Tested?

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context