Implement the new ["span v2" envelope item](<https://develop.sentry.dev/sdk/telemetry/spans/span-protocol/>) in the Rust SDK. This is a public tracking issue for the [internal Linear project](<https://linear.app/getsentry/project/sdk-span-first-rust-912411509fef/issues?layout=list&ordering=priority&grouping=workflowState&subGrouping=none&showCompletedIssues=all&showSubIssues=true&showTriageIssues=false>).
Implement the new "span v2" envelope item in the Rust SDK.
This is a public tracking issue for the internal Linear project.