Balance Views Grouped By Keyset (#652)

* balance view per keyset + relative changes.
    Still lacking: settings changes

* import unit

* fix 0 balance

* settings

---------

Co-authored-by: callebtc <93376500+callebtc@users.noreply.github.com>

tests/test_mint.py

@@ -2,7 +2,7 @@ from typing import List
 
 import pytest
 
-from cashu.core.base import BlindedMessage, Proof
+from cashu.core.base import BlindedMessage, MintKeyset, Proof, Unit
 from cashu.core.crypto.b_dhke import step1_alice
 from cashu.core.helpers import calculate_number_of_blank_outputs
 from cashu.core.models import PostMintQuoteRequest
@@ -218,7 +218,11 @@ async def test_generate_change_promises_returns_empty_if_no_outputs(ledger: Ledg
 
 @pytest.mark.asyncio
 async def test_get_balance(ledger: Ledger):
-    balance = await ledger.get_balance()
+    unit = Unit["sat"]
+    active_keyset: MintKeyset = next(
+        filter(lambda k: k.active and k.unit == unit, ledger.keysets.values())
+    )
+    balance = await ledger.get_balance(active_keyset)
     assert balance == 0