flaky test: tests/extproc/vcr/TestOtelOpenAIChatCompletions_metrics

[mathetake]

    --- FAIL: TestOtelOpenAIChatCompletions_metrics/chat-streaming-detailed-usage (1.12s)
        otel_chat_completions_metrics_test.go:94: 
            	Error Trace:	/Users/runner/work/ai-gateway/ai-gateway/tests/extproc/vcr/otel_chat_completions_metrics_test.go:169
            	            				/Users/runner/work/ai-gateway/ai-gateway/tests/extproc/vcr/otel_chat_completions_metrics_test.go:94
            	Error:      	"0" is not greater than "0"
            	Test:       	TestOtelOpenAIChatCompletions_metrics/chat-streaming-detailed-usage

https://github.com/envoyproxy/ai-gateway/actions/runs/18754655225/job/53503362239