[Python] Scalar arithmetic dunders raise TypeError instead of returning NotImplemented

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

Version: pyarrow 24.0.0 (regression vs. 23.0.1)
Platform: Linux (python 3.12), but not platform-specific

In pyarrow 24.0.0, `pyarrow.lib.Scalar` gained arithmetic dunder methods (`__add__`, `__sub__`, `__mul__`, `__truediv__`, `__pow__`, `__neg__`, and bitwise ops) in `python/pyarrow/scalar.pxi`:

```cython
def __add__(self, object other):
return _pc().call_function('add_checked', [self, other])
```

These implementations unconditionally dispatch to `pyarrow.compute.call_function`, which raises `TypeError` via `_pack_compute_args` when `other` is not a recognized pyarrow / list / tuple / ndarray type:

```
TypeError: Got unexpected argument type for compute function
```

Because a raised `TypeError` does NOT trigger Python's reflected-operator fallback (only a returned `NotImplemented` does, as you can see in [Python data model, §3.3.8](https://docs.python.org/3/reference/datamodel.html#object.__radd__)), any custom class that previously relied on its own `__radd__` / `__rmul__` / `__rsub__` / `__rtruediv__` to handle `pyarrow.Scalar + my_obj` is now broken. The user has no workaround from their side, as `pyarrow.lib.Scalar` is an immutable extension type and cannot be monkey-patched, and virtual subclass registration is not honored by CPython's binary-op dispatch (which uses `PyType_IsSubtype` at the C level).

## Reproducer

```python
import pyarrow

class MyCol:
def __radd__(self, other):
return "MyCol.__radd__ called"

s = pyarrow.scalar(5)
c = MyCol()

# Works on pyarrow <= 23 (Scalar had no __add__, so Python dispatches to MyCol.__radd__)
# Fails on pyarrow >= 24 with:
# TypeError: Got unexpected argument type for compute function
print(s + c)
```

Expected: `"MyCol.__radd__ called"` (or at least a `NotImplemented` return from `Scalar.__add__` so Python can fall back).
Actual: `TypeError` from `_pack_compute_args`.

## Why this matters

Libraries that wrap pyarrow arrays with a richer Python class (like our [Data Curator](https://github.com/KaxaNuk/Data-Curator) library with its `DataColumn` class , but also other downstream projects) have historically been able to make `pyarrow.Scalar + custom_column` work by implementing `__radd__` on their class (and the same for the other reflected-operators). This pattern is now silently broken by an upgrade to 24.0.0, with no opt-out and no Python-level workaround.

### Component(s)

Python