Query trace spans with optional filters.

Each returned span has a duration_ms field (float, milliseconds) — this is the ONLY field guaranteed to be in milliseconds. Spans also carry an attributes map of raw key/value pairs exactly as reported by the instrumenting library: numeric attribute values may be seconds, milliseconds, microseconds, or nanoseconds depending on that library's convention, and nothing in this response labels the unit. Never assume an attribute's numeric value shares duration_ms's unit, and never state a duration in milliseconds unless it came from a duration_ms field.