Make sliced return Iterator[T] instead of Iterator[Sequence[T]]

[ad-chaos]

We make sure that T can be sliced instead for it be a Sequence

Issue reference

Fixes #666

Changes

Adds a SupportsSlicing protocol to check if the type can be sliced instead

Tested against the following code:

from typing import assert_type, Iterator
from array import array
from more_itertools import sliced

assert_type(sliced(str(1), 1), Iterator[str])
assert_type(sliced(list(range(1)), 1), Iterator[list[int]])
assert_type(sliced(tuple(range(1)), 1), Iterator[tuple[int, ...]])
assert_type(sliced(range(1), 1), Iterator[range])
assert_type(sliced((1).to_bytes(), 1), Iterator[bytes])
assert_type(sliced(array("l", [1, 2, 3]), 1), Iterator[array[int]])
sliced({1: 1}, 1)  # error dict[int, int] cannot be assigned to SupportsSlicing[T]
sliced({1}, 1)  # error set[int] cannot be assigned to SupportsSlicing[T]

[bbayles]

I'm confused as to why this is returning Iterator[_T] and not an iterator over things that themselves support slicing?

[ad-chaos]

That is precisely what this is doing. sliced is a generic function that accepts any type that supports slicing and returns an iterator over that type.

[bbayles]

I'm not sure why GitHub Actions is not running tests for this PR. However, when I run the checks myself, I get:

% stubtest more_itertools.more more_itertools.recipes
git oerror: more_itertools.more.SupportsSlicing is not present at runtime
Stub: at line 42
<TypeInfo more_itertools.more.SupportsSlicing>
Runtime:
MISSING

Found 1 error (checked 2 modules)

Could you determine what's causing this and correct it? Thanks.

[ad-chaos]

Done. I also noticed that the _SizedReversible protocol is not used anywhere in the codebase.