[Python] `pa.output_stream()` aborts the process on a read-only buffer

### Describe the bug, including details regarding any error messages, version, and platform.

I've been fuzzing Python C extension modules for a small research project, and this one came up. It reproduces with the binary wheel from a plain `pip install pyarrow`.

### Versions

pyarrow 25.0.0, CPython 3.12.3, Ubuntu 24.04 x86_64.

### Reproducer

```python
import pyarrow as pa

pa.output_stream(pa.py_buffer(b'x'))
```

The process aborts (SIGABRT, exit 134) after printing:

```
/arrow/cpp/src/arrow/io/memory.cc:165: Check failed: buffer->is_mutable() Must pass mutable buffer
[1] 3911118 IOT instruction (core dumped) python
```

`memoryview(b'')` and an empty `py_buffer` do the same:

```python
pa.output_stream(memoryview(b'')) # SIGABRT
pa.output_stream(pa.py_buffer(b'')) # SIGABRT
```

### What does work

A mutable buffer, a path, and `BufferOutputStream` are all fine:

```python
>>> b = pa.allocate_buffer(16)
>>> b.is_mutable
True
>>> type(pa.output_stream(b))

>>> type(pa.output_stream('/tmp/o.bin'))

```

And `pa.py_buffer` is documented to produce a read-only buffer:

```python
>>> pa.py_buffer(b'x').is_mutable
False
```

### Why I think it is worth reporting

`output_stream`'s own docstring lists `buffer` among the accepted source types:

```
source : str, Path, buffer, file-like object
The source to open for writing.
```
so passing a buffer is the documented usage, and a read-only one terminates the interpreter rather than raising.

---

This looks to me like a bug, but I'm not certain it is one, so I'm filing an issue.

### Component(s)

Python