Fix enum serialization

[zaevi]

Motivation and Context

• Fix: PromptMessage Roles do not serialize with lowercase enum values #55

Use JsonStringEnumMemberName for Role and LoggingLevel enum to ensure their serialization is lower-case.

Remove McpClientExtensions.ToJsonValue(LoggingLevel) since serializing issue is fixed.

How Has This Been Tested?

Tested in reproduction for #55.

Breaking Changes

N/A

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

N/A

[Copilot]

Pull Request Overview

This PR fixes enum serialization issues by replacing JsonPropertyName with JsonStringEnumMemberName for the Role and LoggingLevel enums to ensure their JSON output is in lower-case. It also removes the obsolete ToJsonValue extension method from the MCP client, simplifying the request creation for logging level changes.

• Updated the Role enum to use JsonStringEnumMemberName.
• Updated the LoggingLevel enum accordingly.
• Removed the ToJsonValue method from McpClientExtensions and updated its usage.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/ModelContextProtocol/Protocol/Types/Role.cs	Uses JsonStringEnumMemberName for lower-case serialization of Role.
src/ModelContextProtocol/Protocol/Types/LoggingLevel.cs	Uses JsonStringEnumMemberName for each enum value for consistency.
src/ModelContextProtocol/Client/McpClientExtensions.cs	Removes the obsolete ToJsonValue conversion in favor of direct enum usage.

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[stephentoub]

Thanks. Can you please add tests?

[zaevi]

Added basic serialization tests for enums

[eiriktsarpalis]

Added the ContextInclusion enum in the mix since it was missing attributes altogether.

[jeffhandley]

Adding the breaking-change label retroactively during release notes revision.