logreader.py: optimize event loading and sorting in _LogFileReader (#32729)

* improve logfilereader

* less changes

tools/lib/logreader.py

@@ -46,15 +46,15 @@ class _LogFileReader:
 
     ents = capnp_log.Event.read_multiple_bytes(dat)
 
-    _ents = []
+    self._ents = []
     try:
       for e in ents:
-        _ents.append(e)
+        self._ents.append(e)
     except capnp.KjException:
       warnings.warn("Corrupted events detected", RuntimeWarning, stacklevel=1)
 
-    self._ents = list(sorted(_ents, key=lambda x: x.logMonoTime) if sort_by_time else _ents)
-    self._ts = [x.logMonoTime for x in self._ents]
+    if sort_by_time:
+      self._ents.sort(key=lambda x: x.logMonoTime)
 
   def __iter__(self) -> Iterator[capnp._DynamicStructReader]:
     for ent in self._ents: