Pass context wrappers to session methods

[Bortlesboat]

Summary

• add an optional keyword-only wrapper argument to the session protocol and built-in session implementations
• thread the current RunContextWrapper through fresh runs, resumed runs, and rewind/save helpers
• keep third-party session stores backward-compatible by only passing wrapper= when the implementation accepts it, with regression tests for both new and legacy sessions

Testing

• uv run ruff format
• uv run ruff check
• uv run pyright src/agents/memory/session.py src/agents/run.py src/agents/run_internal/run_loop.py src/agents/run_internal/session_persistence.py src/agents/memory/openai_conversations_session.py src/agents/memory/openai_responses_compaction_session.py src/agents/memory/sqlite_session.py src/agents/extensions/memory/advanced_sqlite_session.py src/agents/extensions/memory/async_sqlite_session.py src/agents/extensions/memory/dapr_session.py src/agents/extensions/memory/encrypt_session.py src/agents/extensions/memory/mongodb_session.py src/agents/extensions/memory/redis_session.py src/agents/extensions/memory/sqlalchemy_session.py examples/memory/file_session.py tests/test_agent_as_tool.py tests/test_agent_runner.py tests/test_agent_runner_streamed.py tests/test_session.py tests/test_session_wrapper.py tests/utils/simple_session.py
• uv run mypy src/agents/memory/session.py examples/memory/file_session.py tests/test_session_wrapper.py tests/test_session.py
• uv run pytest tests/test_session_wrapper.py tests/utils/test_simple_session.py tests/test_session.py -k "session_add_items_exception_propagates_in_streamed or test_prepare_input_with_session_passes_wrapper_to_get_items or test_save_result_to_session_passes_wrapper_to_add_items or test_rewind_session_items_passes_wrapper_to_pop_and_cleanup or test_session_helpers_remain_compatible_with_legacy_sessions or test_runner_passes_context_wrapper_to_session_methods"
• uv run pytest tests/test_agent_runner.py -k "wait_for_session_cleanup_retries_after_get_items_error or save_result_to_session_counts_sanitized_openai_items"
• uv run pytest tests/test_agent_runner_streamed.py -k "stream_input_persistence_strips_ids_for_openai_conversation_session"
• uv run python -m py_compile src/agents/memory/session.py src/agents/run.py src/agents/run_internal/run_loop.py src/agents/run_internal/session_persistence.py examples/memory/file_session.py tests/test_session_wrapper.py tests/test_session.py tests/test_agent_runner.py tests/test_agent_runner_streamed.py tests/utils/simple_session.py

Notes

• uv run mypy . --exclude site and uv run pyright --project pyrightconfig.json still report pre-existing baseline issues in optional-dependency example/test modules and sandbox typing; this patch removes the new session-wrapper-specific typing failures.

Closes #2072