fix(lint): remove unused defaultdict import in behavior_monitor #4

Job	Run time
test-dotnet	36s
lint (agent-os)	9s
lint (agent-mesh)	6s
test-integrations-ts	34s
security	32s
lint (agent-compliance)	10s
test (agent-sre, 3.11)	38s
test (agent-os, 3.12)	35s
test (agent-os, 3.10)	41s
test (agent-mesh, 3.12)	53s
test-integrations (a2a-protocol, a2a_agentmesh)	11s
test (agent-hypervisor, 3.12)	33s
lint (agent-hypervisor)	10s
test (agent-compliance, 3.12)	22s
test (agent-os, 3.11)	41s
test (agent-mesh, 3.11)	41s
test (agent-sre, 3.10)	34s
test-integrations (haystack-agentmesh, haystack_agentmesh)	13s
test-integrations (crewai-agentmesh, crewai_agentmesh)	15s
test-integrations (nostr-wot, agentmesh_nostr_wot)	14s
test-integrations (flowise-agentmesh, flowise_agentmesh)	10s
test-integrations (langgraph-trust, langgraph_trust)	14s
test-integrations (langflow-agentmesh, langflow_agentmesh)	13s
test-integrations (dify-plugin, provider)	24s
test-integrations (openai-agents-trust, openai_agents_trust)	28s
test (agent-compliance, 3.11)	20s
test-integrations (mcp-trust-proxy, mcp_trust_proxy)	9s
lint (agent-sre)	10s
test (agent-hypervisor, 3.11)	25s
test (agent-sre, 3.12)	32s
test-integrations (llamaindex-agentmesh, llama_index.agent.agentmesh)	28s
test-integrations (langchain-agentmesh, langchain_agentmesh)	19s
test-integrations (pydantic-ai-governance, pydantic_ai_governance)	10s
test-integrations (openai-agents-agentmesh, openai_agents_agentmesh)	16s
	13m 6s

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