Make gnome sort generic over comparable items

[bpiper02]

Part of #15234

Updates gnome_sort to use a bounded comparable type instead of an untyped list.

Also adds gnome_sort to the shared test covering rejection of non-comparable mixed items.

Validation:

• python -m doctest -v sorts/gnome_sort.py
• python -m pytest tests/test_sorts.py -k "gnome_sort or rejects_non_comparable"
• python -m ruff check sorts/gnome_sort.py tests/test_sorts.py
• python -m ruff format --check sorts/gnome_sort.py tests/test_sorts.py
• python -m compileall sorts/gnome_sort.py

[cclauss]

@priya-sundaram-dev, your review, please.

[priya-sundaram-dev]

LGTM ✅

The subtle part here is the guard change from `lst[i - 1] <= lst[i]` to `not lst[i] < lst[i - 1]`, needed because `Comparable` only supplies `lt`. That rewrite is exactly right:

• Equivalent: for a total order `a <= b` ≡ `not (b < a)`, so the loop advances/swaps identically.
• Stability preserved: equal elements give `lst[i] < lst[i-1] == False` → advance, no swap — same as before.
• Protocol-safe: the body now only ever calls `lt`, matching the `Comparable` bound.

I re-ran it locally: 3000 random lists match `sorted`, and a stability check (2000 runs, wrapper comparing on key only) stays stable. Adding `gnome_sort` to the shared `rejects_non_comparable` coverage is the right move too.

Nice, minimal change — consistent with the rest of #15234.