feat: support togetherAI via `/completions` #4754

Job	Run time
run-core-unit-tests (test_local_client.py)	1m 11s
run-core-unit-tests (test_client.py)	2m 26s
run-core-unit-tests (test_server.py)	1m 2s
run-core-unit-tests (test_managers.py)	49s
run-core-unit-tests (test_tools.py)	56s
run-core-unit-tests (test_o1_agent.py)	1m 10s
run-core-unit-tests (test_tool_rule_solver.py)	59s
run-core-unit-tests (test_agent_tool_graph.py)	55s
misc-unit-tests	1m 37s
	11m 5s

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