Coarser step new mint strikes must align to. A numeric strike must be a whole
multiple of this (the market's referencePrice is the one exception the chain
admits off-grid); otherwise the mint aborts EInvalidAdmissionTick.
The window's anchor strike in USD, or null until the keeper seeds it.
Strike granularity in USD (e.g. 0.01).
One tradeable market as returned by read.markets().