Update ledger *after* pps updates from new trades

Addressing same issue as in #350 where we need to compute position
updates using the *first read* from the ledger **before** we update it
to make sure `Position.lifo_update()` gets called and **not skipped**
because new trades were read as clears entries but haven't actually been
included in update calcs yet.. aka we call `Position.lifo_update()`.

Main change here is to convert `update_ledger()` into a context mngr so
that the ledger write is committed after pps updates using
`pp.update_pps_conf()`..

This is basically a hotfix to #346 as well.

piker/brokers/kraken/broker.py

@@ -18,7 +18,10 @@
 Order api and machinery
 
 '''
-from contextlib import asynccontextmanager as acm
+from contextlib import (
+    asynccontextmanager as acm,
+    contextmanager as cm,
+)
 from functools import partial
 from itertools import chain, count
 from pprint import pformat
@@ -259,7 +262,7 @@ async def trades_dialogue(
         log.info(
             f'Loaded {len(trades)} trades from account `{acc_name}`'
         )
-        trans = await update_ledger(acctid, trades)
+        with open_ledger(acctid, trades) as trans:
             active, closed = pp.update_pps_conf(
                 'kraken',
                 acctid,
@@ -425,7 +428,7 @@ async def handle_order_updates(
                     await ems_stream.send(filled_msg)
 
                 # update ledger and position tracking
-                trans = await update_ledger(acctid, trades)
+                with open_ledger(acctid, trades) as trans:
                     active, closed = pp.update_pps_conf(
                         'kraken',
                         acctid,
@@ -742,7 +745,8 @@ def norm_trade_records(
     return records
 
 
-async def update_ledger(
+@cm
+def open_ledger(
     acctid: str,
     trade_entries: list[dict[str, Any]],
 
@@ -755,8 +759,10 @@ async def update_ledger(
         'kraken',
         acctid,
     ) as ledger:
-        ledger.update(trade_entries)
 
         # normalize to transaction form
         records = norm_trade_records(trade_entries)
-    return records
+        yield records
+
+        # update on exit
+        ledger.update(trade_entries)