Fix duration of httpstream and live debugger spans

[bwoebi]

Yep, these had a duration of 0...

[datadog-datadog-prod-us1]

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 60.64% (-0.01%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 63fee31 | Docs | Datadog PR Page | Give us feedback!}

[pr-commenter]

Benchmarks [ tracer ]

Benchmark execution time: 2026-04-23 17:53:53

Comparing candidate commit 63fee31 in PR branch bob/span-time with baseline commit b7eb412 in branch master.

Found 1 performance improvements and 2 performance regressions! Performance is the same for 189 metrics, 2 unstable metrics.

scenario:MessagePackSerializationBench/benchMessagePackSerialization-opcache

• 🟩 execution_time [-5.293µs; -3.587µs] or [-4.675%; -3.168%]

scenario:SamplingRuleMatchingBench/benchRegexMatching2

• 🟥 execution_time [+53.930ns; +115.270ns] or [+3.674%; +7.854%]

scenario:SpanBench/benchDatadogAPI

• 🟥 execution_time [+1.465µs; +3.091µs] or [+2.246%; +4.740%]