Changing bus instances lifetime

[remimd]

No description provided.

[Copilot]

Pull Request Overview

This PR changes the lifetime of bus instances from singleton to injectable, modifying the dependency injection behavior for command, event, and query buses in the CQ framework.

• Updated bus factory functions to use @injectable instead of @singleton decorators
• Modified FastAPI example documentation to reflect the change from singleton to injectable lifecycle
• Removed unused singleton import from the FastAPI example

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
documentation/fastapi-example.md	Updated example to use @injectable decorator and removed unused singleton import
cq/_core/message.py	Changed bus factory functions from @singleton to @injectable lifecycle management

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