Python: coalesce code interpreter history chunks

[he-yufeng]

Fixes #5793.

Summary

• Coalesce streamed code_interpreter_tool_call and code_interpreter_tool_result content by call_id during response finalization.
• When a later done event carries the full code, keep that full value instead of storing both chunk deltas and the complete script.
• Add a history-provider regression test for the Cosmos-style chunked code interpreter shape.

To verify

• uv run pytest packages\core\tests\core\test_sessions.py::TestHistoryProviderBase::test_after_run_stores_coalesced_code_interpreter_chunks -q --basetemp .tmp\pytest
• uv run pytest packages\core\tests\core\test_sessions.py -q --basetemp .tmp\pytest -p no:cacheprovider
• uv run pytest packages\core\tests\core\test_types.py -q --basetemp .tmp\pytest -p no:cacheprovider
• uv run pytest packages\openai\tests\openai\test_openai_chat_client.py -q -k "code_interpreter" --basetemp .tmp\pytest -p no:cacheprovider
• uv run ruff check packages\core\agent_framework_types.py packages\core\tests\core\test_sessions.py
• uv run ruff format --check packages\core\agent_framework_types.py packages\core\tests\core\test_sessions.py
• uv run mypy packages\core\agent_framework_types.py
• uv run python -m py_compile packages\core\agent_framework_types.py packages\core\tests\core\test_sessions.py
• git diff --check

[Copilot]

Pull request overview

This PR addresses streamed code-interpreter history bloat in the Python core by coalescing code_interpreter_tool_call / code_interpreter_tool_result content items with the same call_id (or item_id) during response finalization, ensuring history providers receive a single aggregated item per logical tool call.

Changes:

• Add response-finalization logic to coalesce code-interpreter tool call/result content by (type, call_id).
• Implement merge behavior that prefers a later “done” event carrying the full code over keeping both deltas and the complete script.
• Add a regression test ensuring history providers store the coalesced code-interpreter content shape.

Reviewed changes

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

File	Description
python/packages/core/agent_framework/_types.py	Adds code-interpreter coalescing/merge helpers and applies them during _finalize_response.
python/packages/core/tests/core/test_sessions.py	Adds a history-provider regression test verifying coalesced code-interpreter chunks are stored as a single content item.