feat: support togetherAI via `/completions` #4757

Job	Run time
run-core-unit-tests (test_local_client.py)	1m 0s
run-core-unit-tests (test_client.py)	2m 29s
run-core-unit-tests (test_server.py)	1m 8s
run-core-unit-tests (test_managers.py)	56s
run-core-unit-tests (test_tools.py)	56s
run-core-unit-tests (test_o1_agent.py)	1m 13s
run-core-unit-tests (test_tool_rule_solver.py)	46s
run-core-unit-tests (test_agent_tool_graph.py)	50s
misc-unit-tests	0s
	9m 18s

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