Use correct schema for client sampling validation when tools are present

[olaservo]

Summary

Fix client-side sampling validation to use CreateMessageResultWithToolsSchema when tools are present in the request, preventing false validation failures for tool_use responses.

Motivation and Context

When a client sampling handler returns tool_use content formatted as an array, validation fails with "Invalid input: expected object, received array". This occurs because the client always validates against CreateMessageResultSchema regardless of whether tools were included in the request.

• CreateMessageResultSchema expects single content blocks (text, image, or audio only)
• CreateMessageResultWithToolsSchema supports array content with tool_use/tool_result blocks

This mirrors the server-side fix from PR #1156, which the client-side code missed.

Fixes #1346

How Has This Been Tested?

Added 5 new integration tests in test/integration/test/client/client.test.ts:

1. Array content with tool_use when request includes tools - Verifies handler can return [{ type: 'tool_use', ... }]
2. Single content when request includes tools - Verifies backwards compatibility
3. Single content when request has no tools - Verifies standard non-tool flow
4. Reject array content when request has no tools - Ensures validation still enforces single content for non-tool requests
5. Array content when request includes toolChoice - Verifies toolChoice also triggers the correct schema

All 483 tests pass.

Breaking Changes

None

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

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commit: eb7aae5