feat: ✨ Introduce DeferredBus

[remimd]

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[Copilot]

Pull Request Overview

This PR introduces a new DeferredBus abstraction that enables deferred execution of commands, queries, and events in FastAPI applications. The implementation leverages FastAPI's BackgroundTasks to execute operations asynchronously without blocking the response.

• Adds a new DeferredBus protocol for deferred execution
• Implements FastAPI-specific deferred bus variants for commands, events, and queries
• Provides dependency injection integration through annotated types

Reviewed Changes

Copilot reviewed 7 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
cq/_core/defer.py	Defines the core DeferredBus protocol with abstract defer method
cq/init.py	Exports the new DeferredBus class in the public API
cq/ext/fastapi.py	Implements FastAPI-specific deferred buses using BackgroundTasks
cq/ext/fastapi.pyi	Provides type aliases for the three deferred bus variants
tests/ext/test_fastapi.py	Adds comprehensive test coverage for the FastAPI deferred bus functionality
pyproject.toml	Adds FastAPI and httpx as test dependencies
documentation/fastapi-example.md	Updates documentation with usage example for the new deferred bus

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