ak.concatenate fails trying to concatenate too many nested arrays

[Superharz]

Version of Awkward Array

2.5.0

Description and code to reproduce

Trying to concatenate too many nested arrays at once results in a crash.
In my case, too many means more than 129 arrays. So close to the int8 range.
As a workaround one can concatenate the arrays in an iterative way by using the concatenate function multiple times.

Minimal example:
This works fine:

a = ak.Array([[1]])
ak.concatenate([a for i in range(128)], axis = -1)

This fails:

a = ak.Array([[1]])
ak.concatenate([a for i in range(130)], axis = -1)

Traceback:

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
File ~\miniforge3\envs\uni4\Lib\site-packages\awkward\contents\numpyarray.py:349, in NumpyArray._carry(self, carry, allow_lazy)
    348 try:
--> 349     nextdata = self._data[carry.data]
    350 except IndexError as err:

IndexError: index 2352008096080 is out of bounds for axis 0 with size 130

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\contents\numpyarray.py", line 349, in _carry
    nextdata = self._data[carry.data]
               ~~~~~~~~~~^^^^^^^^^^^^
IndexError: index 1867296635536 is out of bounds for axis 0 with size 130

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\_dispatch.py", line 62, in dispatch
    next(gen_or_result)
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\operations\ak_concatenate.py", line 61, in concatenate
    return _impl(arrays, axis, mergebool, highlevel, behavior, attrs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\operations\ak_concatenate.py", line 330, in _impl
    out = ak._broadcasting.broadcast_and_apply(
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\_broadcasting.py", line 1027, in broadcast_and_apply
    out = apply_step(
          ^^^^^^^^^^^
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\_broadcasting.py", line 1005, in apply_step
    return continuation()
           ^^^^^^^^^^^^^^
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\_broadcasting.py", line 974, in continuation
    return broadcast_any_list()
           ^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\_broadcasting.py", line 630, in broadcast_any_list
    outcontent = apply_step(
                 ^^^^^^^^^^^
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\_broadcasting.py", line 987, in apply_step
    result = action(
             ^^^^^^^
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\operations\ak_concatenate.py", line 321, in action
    inner = ak.contents.UnionArray.simplified(
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\contents\unionarray.py", line 455, in simplified
    next = contents[0]._carry(index, True)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\flori\miniforge3\envs\uni4\Lib\site-packages\awkward\contents\numpyarray.py", line 351, in _carry
    raise ak._errors.index_error(self, carry.data, str(err)) from err
IndexError: cannot slice NumpyArray (of length 130) with array([            0,             1,             2,             3,
                   4,             5,             6,             7,
                   8,             9,            10,            11,
                  12,            13,            14,            15,
                  16,            17,            18,            19,
                  20,            21,            22,            23,
                  24,            25,            26,            27,
                  28,            29,            30,            31,
                  32,            33,            34,            35,
                  36,            37,            38,            39,
                  40,            41,            42,            43,
                  44,            45,            46,            47,
                  48,            49,            50,            51,
                  52,            53,            54,            55,
                  56,            57,            58,            59,
                  60,            61,            62,            63,
                  64,            65,            66,            67,
                  68,            69,            70,            71,
                  72,            73,            74,            75,
                  76,            77,            78,            79,
                  80,            81,            82,            83,
                  84,            85,            86,            87,
                  88,            89,            90,            91,
                  92,            93,            94,            95,
                  96,            97,            98,            99,
                 100,           101,           102,           103,
                 104,           105,           106,           107,
                 108,           109,           110,           111,
                 112,           113,           114,           115,
                 116,           117,           118,           119,
                 120,           121,           122,           123,
                 124,           125,           126,           127,
       1867296635536, 1867296635536], dtype=int64): index 1867296635536 is out of bounds for axis 0 with size 130

This error occurred while calling

    ak.concatenate(
        [<Array [[1]] type='1 * var * int64'>, <Array [[1]] type='1 * var * i...
        axis = -1
    )

[agoose77]

This is a reasonable thing to expect ak.concatenate to support. Internally we implement concatenation using unions, and unions have a limitation of 128 contents. However, this restriction should not be something that users need to worry about in ak.concatenate unless they end up with >128 distinct content types.