[Python] `MemoryMappedFile().resize()` segfaults when no file has been opened

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

### Summary

`MemoryMappedFile` can be directly constructed without opening a file, and `resize()` on that object terminates the interpreter.
I found this while fuzzing Python C extension modules.
I think this unsupported state should raise a Python exception rather than terminate the process.

### Versions

PyArrow 25.0.1, CPython 3.12.3, Debian 12 x86_64, glibc 2.36

### Reproducer

```python
import pyarrow as pa

pa.MemoryMappedFile().resize(0)
```

```console
Segmentation fault (core dumped)
```

### ASan/UBSan result

I built PyArrow 25.0.0 from source with Clang 18 using ASan and UBSan instrumentation.
UBSan reports a member call on a null `arrow::io::MemoryMappedFile` in the generated wrapper:

```text
build/lib.cpp:252525:86: runtime error:
member call on null pointer of type 'arrow::io::MemoryMappedFile'

#0 pyarrow.lib.MemoryMappedFile.resize(...)
build/lib.cpp:252525:86

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
build/lib.cpp:252525:86
```

ASan then reports a read from address `0x28` on the same path.
The sanitizer process exits with code 134 after ASan aborts.

### Component(s)

Python

Start by running the provided Python reproducer for pyarrow.lib.MemoryMappedFile.resize and inspect the generated wrapper path shown in build/lib.cpp:252525. Confirm the no-file state is handled without terminating the interpreter; done means the call raises a Python exception instead of segfaulting, with coverage for this reproducer.

Written by the indexing model from the issue text.