kraken: `Pair.costmin` is now optional?

Some pairs don't seem to define it but it's not listed as deprecated on
official API page (new one now linked in type def's doc string).

piker/brokers/kraken/symbols.py

@@ -21,7 +21,6 @@ Symbology defs and search.
 from decimal import Decimal
 
 import tractor
-from rapidfuzz import process as fuzzy
 
 from piker._cacheables import (
     async_lifo_cache,
@@ -41,8 +40,13 @@ from piker.accounting._mktinfo import (
 )
 
 
-# https://www.kraken.com/features/api#get-tradable-pairs
 class Pair(Struct):
+    '''
+    A tradable asset pair as schema-defined by,
+
+    https://docs.kraken.com/api/docs/rest-api/get-tradable-asset-pairs
+
+    '''
     xname: str  # idiotic bs_mktid equiv i guess?
     altname: str  # alternate pair name
     wsname: str  # WebSocket pair name (if available)
@@ -53,7 +57,6 @@ class Pair(Struct):
     lot: str  # volume lot size
 
     cost_decimals: int
-    costmin: float
     pair_decimals: int  # scaling decimal places for pair
     lot_decimals: int  # scaling decimal places for volume
 
@@ -79,6 +82,7 @@ class Pair(Struct):
     tick_size: float  # min price step size
     status: str
 
+    costmin: str|None = None  # XXX, only some mktpairs?
     short_position_limit: float = 0
     long_position_limit: float = float('inf')