Support lot tick size (mostly for crypto)

piker/data/__init__.py

@@ -276,6 +276,7 @@ async def open_feed(
             symbol = Symbol(
                 key=sym,
                 tick_size=si.get('price_tick_size', 0.01),
+                lot_tick_size=si.get('lot_tick_size', 0.0),
             )
             symbol.broker_info[brokername] = si
 

piker/data/_source.py

@@ -97,6 +97,9 @@ class Symbol(BaseModel):
         """
         return float_digits(self.tick_size)
 
+    def lot_digits(self) -> int:
+        return float_digits(self.lot_tick_size)
+
     def nearest_tick(self, value: float) -> float:
         """Return the nearest tick value based on mininum increment.