[BUG] plot1d doesn't work with IntCat axis

[andrzejnovak]

Describe the bug

plo1d (with overlay for a categorical axis) only works for StrCat but not for IntCat

Steps to reproduce

import hist
import numpy as np

h2 = hist.new.Reg(10, 0, 10).IntCat([], growth=True).Weight().fill(np.random.normal(5, 2, int(1e6)), np.random.choice([1,2,3,4], int(1e6)))
h2.plot1d()

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
Cell In[13], line 1
----> 1 h2.plot1d()

File ~/software/micromamba/envs/def/lib/python3.11/site-packages/hist/basehist.py:424, in BaseHist.plot1d(self, ax, overlay, **kwargs)
    422 cat_ax = self.axes[overlay]
    423 cats = cat_ax if cat_ax.traits.discrete else np.arange(len(cat_ax.centers))
--> 424 d1hists = [self[{overlay: cat}] for cat in cats]
    425 if "label" in kwargs:
    426     if not isinstance(kwargs["label"], str) and len(kwargs["label"]) == len(
    427         cats
    428     ):

File ~/software/micromamba/envs/def/lib/python3.11/site-packages/hist/basehist.py:424, in <listcomp>(.0)
    422 cat_ax = self.axes[overlay]
    423 cats = cat_ax if cat_ax.traits.discrete else np.arange(len(cat_ax.centers))
--> 424 d1hists = [self[{overlay: cat}] for cat in cats]
    425 if "label" in kwargs:
    426     if not isinstance(kwargs["label"], str) and len(kwargs["label"]) == len(
    427         cats
    428     ):

File ~/software/micromamba/envs/def/lib/python3.11/site-packages/hist/basehist.py:324, in BaseHist.__getitem__(self, index)
    317 def __getitem__(  # type: ignore[override]
    318     self: T, index: IndexingExpr
    319 ) -> T | float | bh.accumulators.Accumulator:
    320     """
    321     Get histogram item.
    322     """
--> 324     return super().__getitem__(self._index_transform(index))

File ~/software/micromamba/envs/def/lib/python3.11/site-packages/boost_histogram/_internal/hist.py:842, in Histogram.__getitem__(self, index)
    838 def __getitem__(  # noqa: C901
    839     self: H, index: IndexingExpr
    840 ) -> Union[H, float, Accumulator]:
--> 842     indexes = self._compute_commonindex(index)
    844     # If this is (now) all integers, return the bin contents
    845     # But don't try *dict!
    846     if not hasattr(indexes, "items") and all(
    847         isinstance(a, SupportsIndex) for a in indexes
    848     ):

File ~/software/micromamba/envs/def/lib/python3.11/site-packages/boost_histogram/_internal/hist.py:750, in Histogram._compute_commonindex(self, index)
    748         indexes[i] = [self._compute_uhi_index(ind, i) for ind in indexes[i]]
    749     else:
--> 750         indexes[i] = self._compute_uhi_index(indexes[i], i)
    752 return indexes

File ~/software/micromamba/envs/def/lib/python3.11/site-packages/boost_histogram/_internal/hist.py:709, in Histogram._compute_uhi_index(self, index, axis)
    707 if isinstance(index, SupportsIndex):
    708     if abs(int(index)) >= self._hist.axis(axis).size:
--> 709         raise IndexError("histogram index is out of range")
    710     return int(index) % self._hist.axis(axis).size
    712 return index

IndexError: histogram index is out of range