[codex] Add incremental chat completion traces #752

Job	Run time
build-and-smoke-freebuff-windows	2m 23s
build-freebuff	1m 7s
e2e-ads-behavior	1m 2s
e2e-version	53s
e2e-terminal-command	57s
e2e-startup	1m 6s
e2e-code-edit	58s
e2e-slash-commands	1m 6s
e2e-help-command	1m 9s
e2e-agent-startup	2m 12s
	12m 53s

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