Since we're not quite yet using automatic typed msging from
`tractor`/`msgspec` (i.e. still manually decoding order ctl msgs from
built-in types..`dict`s still not `msgspec.Struct`) this adds the
appropriate typecasting ops to ensure the required precision is attained
prior to processing and/or submission to a brokerd backend service.
For the `.clearing._ems`,
- flip all `trigger_price` previously presumed to be `float` to just
the field-identical `price: Decimal` and ensure we cast to `float`
for any `trigger_price` usage, like before passing to `mk_check()`.
For `.ui.order_mode.OrderMode`,
- add a new `.curr_mkt: MktPair` convenience property to get the
chart-active value.
- ensure we always use the `.curr_mkt.quantize() -> Decimal` before
setting any IPC-msg's `.price` field!
- always cast `float(Order.price)` before use in setting line-levels.
- don't bother setting `Order.symbol` to a (now fully removed) `Symbol`
instance since it's not really required-for-use anywhere; leaving it
a `str` (per the type-annot) is fine for now?
aaf2dbcd79