[codex] Add incremental chat completion traces #754

Job	Run time
build-and-smoke-freebuff-windows	2m 16s
build-freebuff	1m 21s
e2e-ads-behavior	1m 3s
e2e-agent-startup	2m 16s
e2e-terminal-command	1m 12s
e2e-startup	1m 1s
e2e-version	1m 14s
e2e-code-edit	1m 10s
e2e-help-command	1m 21s
e2e-slash-commands	1m 2s
	13m 56s

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