fix: Tasks outside runs

[monoxgas]

• Add the ability for tasks to execute outside of runs without raising errors in common __call__ scenarios

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Generated Summary:

• Updated metric value type in documentation from float to float | None to indicate optional values.
• Changed run and object linking method usage in examples from run.link_objects() to dreadnode.link_objects(), ensuring consistency across usage.
• Introduced checks for optional dependencies (like audio, image, and video processing) with clear error messages upon import failures, improving user experience.
• Updated method signatures and examples to use dreadnode methods directly instead of instance methods for clarity and simplicity.
• Modified string cleaning function to support @ character in addition to /, enhancing its utility in various contexts.
• Added a span management feature in the Task class, helping to handle trace spans more effectively during asynchronous call handling.

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