Python: consume Anthropic beta flags

[he-yufeng]

Summary

• consume per-run additional_beta_flags into the Anthropic beta set without forwarding it as a raw request kwarg
• add a regression test for _prepare_options(...)

Fixes #5764.

To verify

• uv run pytest tests/test_anthropic_client.py -q
• uv run ruff check agent_framework_anthropic tests/test_anthropic_client.py
• uv run ruff format --check agent_framework_anthropic tests/test_anthropic_client.py
• uv run pyright
• uv run mypy --config-file pyproject.toml agent_framework_anthropic
• python -m py_compile agent_framework_anthropic\_chat_client.py tests\test_anthropic_client.py

[Copilot]

Pull request overview

Fixes an Anthropic client integration issue where per-run additional_beta_flags were being forwarded as a raw request kwarg (causing Anthropic SDK TypeErrors) instead of being consumed into the betas set used for the request.

Changes:

• Remove additional_beta_flags from the final run_options after it has been merged into betas.
• Add a regression test ensuring additional_beta_flags is consumed into betas and not forwarded.

Reviewed changes

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

File	Description
python/packages/anthropic/agent_framework_anthropic/_chat_client.py	Pops additional_beta_flags from run_options after preparing betas to prevent forwarding unsupported kwargs.
python/packages/anthropic/tests/test_anthropic_client.py	Adds a regression test to verify additional_beta_flags is consumed into betas and removed from run_options.