feat: added swarm and graph spans

[poshinchen]

Description

Add swarm and graph span.

• task can either be str or list of contentBlock, and it'll be serialized in the span.event_attributes.

NOTE: graph output hasn't been added as it needs validations

Example output

Swarm: https://us.cloud.langfuse.com/project/cmbb4s57d01xiad07eex8qvrl/traces/86ea0dbb4fef507c20af024ff249fec9?timestamp=2025-07-14T14:56:32.189Z&display=details

Graph: https://us.cloud.langfuse.com/project/cmbb4s57d01xiad07eex8qvrl/traces/3336a722fe1f89beadd523d8931f9c0d?timestamp=2025-07-14T15:07:39.573Z&display=details

Type of Change

New feature

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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