Returns the current oracle price for every supported trading pair.

The oracle publishes a USD price per asset, not per pair. This endpoint joins those
feeds against the supported symbol list and derives each pair as base_usd / quote_usd,
so you do not have to divide two feeds yourself.

Assets flagged as stablecoins in the instruments catalog (e.g. USDA) are valued at
their 1.00 USD peg when the oracle publishes no feed for them. When a live oracle feed
does exist for such an asset, that feed is used instead of the peg.

A pair is omitted from the map when either side has no usable USD rate. Treat a
missing key as "not priced yet" rather than zero.

Note that these are oracle valuations, not traded prices. For the last traded price
use /api/v1/market/ticker.