fix(telemetry): prevent double counting of usage metrics

[rajib76]

Description

This is a fix for the below bug:
_[BUG] OpenTelemetry token/cost metrics double-counted in Langfuse due to duplicate reporting on parent and child spans #1267

Related Issues

#1267

Documentation PR

Type of Change

Bug fix

Bug fix
New feature
Breaking change
Documentation update
Other (please describe):

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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[rajib76]

I created a new pull request for this pull request# 1327