Refactors docket/background task support to be encapsulated within each
component rather than requiring external coordination:
- Move task_config to FastMCPComponent base class (default: forbidden)
- Add register_with_docket(docket) method that components use to register
themselves, checking task_config internally
- Add add_to_docket() method that handles component-specific calling
conventions (splatted kwargs vs positional dict)
- Simplify server registration to just call component.register_with_docket()
- Update task handlers to use component.add_to_docket()
This enables custom Tool/Resource/Prompt subclasses to support background
tasks by setting task_config and optionally overriding the docket methods.
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