Chain trading activity

Chain-level trading activity, for the chain itself rather than any one token — the only endpoint here that takes no token or wallet address. Figures cover four TRAILING windows that NEST inside one another: h4 includes h1, h12 includes h4, h24 includes h12. They are cumulative, not consecutive buckets, so they must not be summed. 24 hours is the longest window published; there is no 7-day or 30-day figure. Every field is null when nothing could be established for the chain — never 0, which here would claim a chain saw no trading at all. asOf reports the freshness of the INDEXED DATA the figures were computed from — the block and instant the source had last processed when it answered, never the instant this request was made, and null when the source could not say. A cache may sit in front of this endpoint, so a caller cannot otherwise tell a just-measured number from one served minutes ago. asOf.at is the SOURCE clock, not ours: measured live, some chains reported an instant up to a second AHEAD of this service, so now minus asOf.at can legitimately be slightly negative and should be read as zero age rather than as an error.