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GH-40560: [Python] RunEndEncodedArray.from_arrays: bugfix for Array arguments (#40560) (#41093)

### Rationale for this change

The documentation suggests that `RunEndEncodedArray.from_arrays` takes two `Array` parameters, as would be expected of a `from_arrays` method. However, if given an `Array` instance for the `run_ends` parameter, it errors because `Array.__getitem__` returns a pyarrow scalar instead of a native Python integer.

### What changes are included in this PR?

* Handle `Array` parameters for `run_ends` by unconditionally coercing the logical length to a pyarrow scalar, then to a Python native value.

### Are these change tested?

Yes. Augmented the existing unit tests to test with `Array` as well as Python lists, and check that the data types of the `Array` instances correctly carry over to the data type of the `RunEndEncodedArray`.

### Are there any user-facing changes?

Not apart from the bugfix; this was the minimum necessary change to make `Array` parameters work. `RunEndEncodedArray.from_arrays` continues to support e.g. python lists as before.

* GitHub Issue: #40560

Authored-by: Hemidark <support@hemidark.net>
Signed-off-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>