Assume float timestamps are UTC.

`time.time()` returns unix timestamp in utc, so this seems to be a
reasonable assumption.

src/neptune_scale/api/attribute.py

@@ -2,7 +2,10 @@
 import itertools
 import threading
 import warnings
-from datetime import datetime
+from datetime import (
+    datetime,
+    timezone,
+)
 from typing import (
     Any,
     Callable,
@@ -95,7 +98,7 @@ def log(
         if timestamp is None:
             timestamp = datetime.now()
         elif isinstance(timestamp, (float, int)):
-            timestamp = datetime.fromtimestamp(timestamp)
+            timestamp = datetime.fromtimestamp(timestamp, timezone.utc)
 
         with self._lock:
             self._verify_and_update_metrics_state(step, metrics)

tests/unit/test_attribute.py

@@ -1,3 +1,4 @@
+import time
 from datetime import datetime
 from unittest.mock import Mock
 
@@ -68,8 +69,9 @@ def test_tags(run, store):
 
 
 def test_series(run, store):
-    run["my/series"].append(1, step=1, timestamp=10)
-    store.log.assert_called_with(metrics={"my/series": 1}, step=1, timestamp=10)
+    timestamp = time.time()
+    run["my/series"].append(1, step=1, timestamp=timestamp)
+    store.log.assert_called_with(metrics={"my/series": 1}, step=1, timestamp=timestamp)
 
     run["my/series"].append({"foo": 1, "bar": 2}, step=2)
     store.log.assert_called_with(metrics={"my/series/foo": 1, "my/series/bar": 2}, step=2, timestamp=None)