Test suite verified green against both 0.2.2 and 0.6.0 (the Schema
classes we consume — TextContent, CallToolResult, ToolAnnotations —
are unchanged). Also fix a flaky timing assertion in EventTest.

Unblocks drupal.org mcp_tools#3589053 (coexistence with modules
requiring mcp/sdk 0.6).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>