Make `copy.deepcopy` faster for `slice` objects

## `slice`

Right now `slice` objects are deepcopied using `__reduce__` defined as:
https://github.com/python/cpython/blob/26ff43625ed7bf09542ad8f149cb6af710b41e15/Objects/sliceobject.c#L559-L563

It is one of last branches of `deepcopy` logic:
https://github.com/python/cpython/blob/26ff43625ed7bf09542ad8f149cb6af710b41e15/Lib/copy.py#L120-L157

But, since `slice` is an immutable type without nested structures, we can optimize its `deepcopy` as:

```python
d[slice] = _deepcopy_atomic
```

Before:

```
» pyperf timeit --setup 'from copy import deepcopy; s = slice(1,10,2)' 'deepcopy(s)'
.....................
Mean +- std dev: 3.46 us +- 0.18 us
```

After:

```
» pyperf timeit --setup 'from copy import deepcopy; s = slice(1,10,2)' 'deepcopy(s)'
.....................
Mean +- std dev: 277 ns +- 3 ns
```

Looks like a good speedup for just a single line!
Noticed while working on #100815 

PR is incoming.


### Linked PRs
* gh-100818

	def deepcopy(x, memo=None, _nil=[]):
	"""Deep copy operation on arbitrary Python objects.

	See the module's __doc__ string for more info.
	"""

	if memo is None:
	memo = {}

	d = id(x)
	y = memo.get(d, _nil)
	if y is not _nil:
	return y

	cls = type(x)

	copier = _deepcopy_dispatch.get(cls)
	if copier is not None:
	y = copier(x, memo)
	else:
	if issubclass(cls, type):
	y = _deepcopy_atomic(x, memo)
	else:
	copier = getattr(x, "__deepcopy__", None)
	if copier is not None:
	y = copier(memo)
	else:
	reductor = dispatch_table.get(cls)
	if reductor:
	rv = reductor(x)
	else:
	reductor = getattr(x, "__reduce_ex__", None)
	if reductor is not None:
	rv = reductor(4)
	else:
	reductor = getattr(x, "__reduce__", None)
	if reductor:
	rv = reductor()

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Make `copy.deepcopy` faster for `slice` objects #100817

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	static PyObject *
	slice_reduce(PySliceObject* self, PyObject *Py_UNUSED(ignored))
	{
	return Py_BuildValue("O(OOO)", Py_TYPE(self), self->start, self->stop, self->step);
	}

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Make copy.deepcopy faster for slice objects #100817

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Make `copy.deepcopy` faster for `slice` objects #100817

`slice`