Add evalbuff: iterative agent improvement via docs optimization #5993

Job	Run time
build-and-check	3m 10s
test-integration-packages/internal	1m 7s
test-integration-packages/billing	1m 16s
test-integration-cli	42s
test-integration-packages/agent-runtime	40s
test-integration-common	50s
test-integration-sdk	1m 34s
test-integration-web	42s
test-sdk	53s
test-.agents	49s
test-web	55s
test-packages/internal	48s
test-packages/billing	47s
test-common	42s
test-cli	50s
test-packages/agent-runtime	51s
	16m 36s

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