feat: move HTML rendering of messages into `LettaResponse` and update notebook #4643

Job	Run time
run-core-unit-tests (test_local_client.py)	1m 16s
run-core-unit-tests (test_client.py)	2m 25s
run-core-unit-tests (test_server.py)	1m 33s
run-core-unit-tests (test_managers.py)	1m 16s
run-core-unit-tests (test_tools.py)	1m 21s
run-core-unit-tests (test_o1_agent.py)	1m 43s
run-core-unit-tests (test_tool_rule_solver.py)	1m 11s
run-core-unit-tests (test_agent_tool_graph.py)	1m 14s
misc-unit-tests	1m 24s
	13m 23s

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