Fix Python PointFilter HDF5 deserialization and next-event estimator type

PointFilter lacked from_hdf5() and get_pandas_dataframe() overrides.
The base Filter.from_hdf5() passed a flat numpy array to PointFilter.__init__
which expects Sequence[tuple], causing TypeError. The base
get_pandas_dataframe() used np.repeat on the nested tuple structure,
causing ValueError.

Also add 'next-event' to ESTIMATOR_TYPES so the Tally.estimator setter
accepts the value read from statepoint files.

Fixes:
- Add PointFilter.from_hdf5() that reconstructs (pos, r0) tuples from
  flat HDF5 bins array.
- Add PointFilter.get_pandas_dataframe() that formats detector positions
  as readable string labels.
- Add 'next-event' to ESTIMATOR_TYPES set in tallies.py.

Author: zxkjack123

openmc/filter.py

@@ -834,6 +834,28 @@ def bins(self, bins):
             cv.check_length(f'bins[{i}][0]', item[0], 3, 3)
             cv.check_type(f'bins[{i}][1]', item[1], Real)
         self._bins = bins
+
+    @classmethod
+    def from_hdf5(cls, group, **kwargs):
+        filter_id = int(group.name.split('/')[-1].lstrip('filter '))
+        flat = group['bins'][()]
+        # Reconstruct tuple structure: every 4 values = (x, y, z, r0)
+        bins = []
+        for i in range(0, len(flat), 4):
+            pos = (float(flat[i]), float(flat[i+1]), float(flat[i+2]))
+            r0 = float(flat[i+3])
+            bins.append((pos, r0))
+        out = cls(bins, filter_id=filter_id)
+        out._num_bins = group['n_bins'][()]
+        return out
+
+    def get_pandas_dataframe(self, data_size, stride, **kwargs):
+        import pandas as pd
+        labels = [f"({p[0]}, {p[1]}, {p[2]}) R0={r}" for (p, r) in self.bins]
+        filter_bins = np.repeat(labels, stride)
+        tile_factor = data_size // len(filter_bins)
+        filter_bins = np.tile(filter_bins, tile_factor)
+        return pd.DataFrame({self.short_name.lower(): filter_bins})
 
     def to_xml_element(self):
         """Return XML Element representing the Filter.

openmc/tallies.py

@@ -36,7 +36,7 @@
 _FILTER_CLASSES = (openmc.Filter, openmc.CrossFilter, openmc.AggregateFilter)
 
 # Valid types of estimators
-ESTIMATOR_TYPES = {'tracklength', 'collision', 'analog'}
+ESTIMATOR_TYPES = {'tracklength', 'collision', 'analog', 'next-event'}
 
 
 class Tally(IDManagerMixin):