Add OpenCode runner to BuffBench (#615) #563

Job	Run time
build-and-smoke-freebuff-windows	2m 26s
build-freebuff	1m 8s
e2e-agent-startup	2m 19s
e2e-version	53s
e2e-ads-behavior	1m 7s
e2e-startup	1m 23s
e2e-code-edit	1m 2s
e2e-slash-commands	56s
e2e-terminal-command	55s
e2e-help-command	1m 19s
	13m 28s

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