fix: Add usage data integration to #760 feature addition

[seratch]

This pull request enhances #760 enhancement:

• Add an endpoint field to RequestUsage and populate requestUsageEntries for both responses.create and responses.compact.
• Change runCompaction to return CompactionResult | null so compaction usage is merged into the runner’s aggregated usage when it runs.
• Update OpenAI Responses model/compaction session handling and serialization schemas, and refresh tests to assert requestUsageEntries with endpoint metadata.

Since this feature is not yet released, there is no breaking change.

[changeset-bot]

🦋 Changeset detected

Latest commit: 9d8f8f0

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
@openai/agents-openai	Patch
@openai/agents-core	Patch
@openai/agents	Patch
@openai/agents-extensions	Patch
@openai/agents-realtime	Patch

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