Expose per-completion-call usage in agent responses (#1787) #43

Job	Run time
run-ci / stable / test	5m 34s
run-ci / stable / clippy	1m 39s
run-ci / stable / doc	1m 20s
run-ci / stable / check rig-core wasm target	38s
run-ci / stable / fmt	26s
Release-plz	1m 26s
	11m 3s

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