Returns exchange statistics with optional symbol filtering.
Notes:
symbol omitted) are cached with 600s TTL24h -> 1d1w -> 7d1m -> 30d3m -> 90d365d -> 1ysymbol) are cached with 600s TTL24h → 1d, 1w → 7d, 1m → 30d, 3m → 90d, 365d → 1yCanonical period value.
If omitted or invalid, defaults to 1d.
1d, 7d, 30d, 90d, 1y, all Optional symbol filter (e.g. BTC-USD)
"BTC-USD"