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GH-40153: [Python][C++] Fix large file handling on 32-bit Python build (#40176)

### Rationale for this change

Python large file tests fail on 32-bit platforms.

### What changes are included in this PR?

1. Fix passing `int64_t` position to the Python file methods when a Python file object is wrapped in an Arrow `RandomAccessFile`
2. Disallow creating a `MemoryMappedFile` spanning more than the `size_t` maximum, instead of silently truncating its length

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.

* GitHub Issue: #40153

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>