feat: checkpoint-based state, breakpoint system, and multi-agent streaming fixes

[cristipufu]

Summary

feat: replace session-based state with checkpoints, add breakpoint system

• Replace SqliteSessionStore with checkpoint-based persistence using the Agent Framework's CheckpointStorage protocol (SqliteCheckpointStorage, ScopedCheckpointStorage)
• Add executor-level breakpoints that work with all agent types (RawAgent, Agent) by wrapping executor.execute() instead of using middleware
• Add HITL interrupt support, resumable storage with KV store, and session persistence via runtime_kv table
• Update samples: replace quickstart-agent/multi-agent with quickstart-workflow/hitl-workflow/concurrent

feat: exclude handoff tools from graph tool nodes

• Handoff tools (handoff_to_) are already represented as edges between agent nodes — filter them out so the graph only shows non-handoff tools in tool nodes

fix: extract tool state events from executor_completed when output events are filtered

• In multi-agent workflows like GroupChat, participant agents are not output executors, so their tool call output events get dropped. Fall back to extracting tool events from executor_completed data when no output events were seen for that executor

fix: resolve breakpoint infinite loop in debug streaming with cyclic topologies

• Add checkpoint advancement detection to _get_breakpoint_skip() to correctly handle cyclic graphs (GroupChat, handoffs) where executors are visited on every cycle
• Merge interrupt.py into breakpoints.py (AgentInterruptException, BreakpointMiddleware)
• Add breakpoint integration tests for all sample topologies (group-chat, quickstart-workflow, concurrent, handoff, hitl-workflow)
• Move agent-framework-orchestrations to main dependencies, bump version to 0.0.5

Test plan

• All 95 tests pass
• mypy --config-file pyproject.toml . → 0 errors
• ruff check . → 0 errors
• Integration tests cover all sample topologies with cyclic/acyclic graphs

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