AnonTaskStats.post_init fails when worker returns numpy.int64

[MathysRennela]

AnonTaskStats.post_init fails when worker returns numpy integer scalars (np.int64) — causes 'Worker failed' in CollectionManager.

Minimal reproducer

import numpy as np
import sinter
from sinter._data._anon_task_stats import AnonTaskStats

# Constructing AnonTaskStats with numpy int64 triggers AssertionError in __post_init__
a = AnonTaskStats(shots=np.int64(10), errors=np.int64(0), discards=np.int64(0), seconds=np.float64(0.0), custom_counts={})
print(a)

This happens when using sinter under pytest, since workers sometimes return numpy.int64 for fields like errors/shots.
This leads to an AssertionError on isinstance(self.errors, int). The CollectionManager aborts with "Worker failed".
This only happens with multiprocessing.