Remove unnecessary negative remainder check in timestamp conversion

Python's modulo operator always returns non-negative result when divisor
is positive, regardless of dividend sign. The check for remainder_ms < 0
is therefore unnecessary in both Python and Cython implementations.

Co-authored-by: Lorak-mmk <5958117+Lorak-mmk@users.noreply.github.com>

Author: Copilot

cassandra/cython_utils.pyx

@@ -70,12 +70,9 @@ cdef datetime_from_timestamp_ms(int64_t timestamp_ms):
     :param timestamp_ms: a unix timestamp, in milliseconds
     """
     # Break down milliseconds into components to avoid float conversion
+    # Cython's % operator uses Python semantics, always returns non-negative for positive divisor
     cdef int64_t timestamp_seconds = timestamp_ms // 1000
     cdef int64_t remainder_ms = timestamp_ms % 1000
-    # Handle negative timestamps correctly
-    if remainder_ms < 0:
-        remainder_ms += 1000
-        timestamp_seconds -= 1
 
     cdef int days = <int> (timestamp_seconds // DAY_IN_SECONDS)
     cdef int64_t days_in_seconds = (<int64_t> days) * DAY_IN_SECONDS

cassandra/util.py

@@ -73,13 +73,9 @@ def datetime_from_timestamp_ms(timestamp_ms):
     :param timestamp_ms: a unix timestamp, in milliseconds (as integer)
     """
     # Break down milliseconds into components to avoid float conversion
+    # Python's % operator always returns non-negative result for positive divisor
     timestamp_seconds = timestamp_ms // 1000
     remainder_ms = timestamp_ms % 1000
-    # Handle negative timestamps correctly
-    if remainder_ms < 0:
-        remainder_ms += 1000
-        timestamp_seconds -= 1
-    
     microseconds = remainder_ms * 1000
     dt = DATETIME_EPOC + datetime.timedelta(seconds=timestamp_seconds, microseconds=microseconds)
     return dt