Use `force_mkt` override in paper pps updates

When processing paper trades ledgers we normally won't have specific
`MktPair` info for the backend market we're simulating, as such we
need to look up this info when updating pps.toml files such that we
get precision info correct (particularly in the case of cryptos!) and
can also run paper ledger processing without running the simulated
clearing loop. In order to make it happen we lookup any `get_mkt_info()`
ep on the backend and pass the output to the `force_mkt` input of the
`PpTable.update_from_trans()` method.

piker/accounting/_pos.py

@@ -504,7 +504,7 @@ class PpTable(Struct):
         trans: dict[str, Transaction],
         cost_scalar: float = 2,
 
-        mkt: MktPair | None = None,
+        force_mkt: MktPair | None = None,
 
     ) -> dict[str, Position]:
 
@@ -523,7 +523,7 @@ class PpTable(Struct):
 
             # template the mkt-info presuming a legacy market ticks
             # if no info exists in the transactions..
-            mkt: MktPair | Symbol | None = mkt or t.sys
+            mkt: MktPair | Symbol | None = force_mkt or t.sys
             if not mkt:
                 mkt = MktPair.from_fqme(
                     fqme,

piker/clearing/_paper_engine.py

@@ -34,9 +34,13 @@ import pendulum
 import trio
 import tractor
 
+from ..brokers import get_brokermod
 from .. import data
 from ..data.types import Struct
-from ..accounting._mktinfo import Symbol
+from ..accounting._mktinfo import (
+    Symbol,
+    MktPair,
+)
 from ..accounting import (
     Position,
     PpTable,
@@ -545,8 +549,31 @@ async def trades_dialogue(
             'paper',
         ) as ledger
     ):
+        # attempt to get market info from the backend instead of presuming
+        # the ledger entries have everything correct.
+        # TODO: how to process ledger info from backends?
+        # - should we be rolling our own actor-cached version of these
+        # client API refs or using portal IPC to send requests to the
+        # existing brokerd daemon?
+        # - alternatively we can possibly expect and use
+        # a `.broker.norm_trade_records()` ep?
+        mkt: MktPair | None = None
+        brokermod = get_brokermod(broker)
+        gmi = getattr(brokermod, 'get_mkt_info', None)
+        if gmi:
+            mkt, pair = await brokermod.get_mkt_info(
+                fqme.rstrip(f'.{broker}'),
+            )
+
         # update pos table from ledger history
-        ppt.update_from_trans(ledger.to_trans())
+        ppt.update_from_trans(
+            ledger.to_trans(),
+
+            # NOTE: here we pass in any `MktPair` provided by the
+            # backend broker instead of assuming the pps.toml contains
+            # the correct contents!
+            force_mkt=mkt
+        )
 
         pp_msgs: list[BrokerdPosition] = []
         pos: Position