Implements client support for MCP Tasks via an adapter model that handles both tool execution modes identically.
This can later be hooked into event handlers in a more intelligent way, but this unblocks support for simply invoking task-augmented tools.

Keep error handling and edge case tests (timeout, failure status, config).
Also remove unused create_tool_with_task_support helper and trim task_echo_server.

Reduces PR diff from 1433 to 969 lines (under 1000 limit).

…odule

- Create mcp_tasks.py module with TasksConfig and task-related constants
- Remove ExperimentalConfig wrapper class from mcp_client.py
- Change MCPClient parameter from experimental to tasks (direct TasksConfig)
- Export TasksConfig at module level in __init__.py
- Update all unit and integration tests to use simplified API

- Rename MCPClient parameter for clarity
- Add MCP Tasks documentation to AGENTS.md
- Fix timeout logging to use total_seconds()