Implement blank_line_after_nested_stub_class preview style (#9155)

## Summary

This PR implements the `blank_line_after_nested_stub_class` preview
style in the formatter.

The logic is divided into 3 parts:
1. In between preceding and following nodes at top level and nested
suite
2. When there's a trailing comment after the class
3. When there is no following node from (1) which is the case when it's
the last or the only node in a suite

We handle (3) with `FormatLeadingAlternateBranchComments`.

## Test Plan

- Add new test cases and update existing snapshots
- Checked the `typeshed` diff

fixes: #8891

crates/ruff_python_formatter/src/preview.rs

@@ -48,6 +48,13 @@ pub(crate) const fn is_wrap_multiple_context_managers_in_parens_enabled(
     context.is_preview()
 }
 
+/// Returns `true` if the [`blank_line_after_nested_stub_class`](https://github.com/astral-sh/ruff/issues/8891) preview style is enabled.
+pub(crate) const fn is_blank_line_after_nested_stub_class_enabled(
+    context: &PyFormatContext,
+) -> bool {
+    context.is_preview()
+}
+
 /// Returns `true` if the [`module_docstring_newlines`](https://github.com/astral-sh/ruff/issues/7995) preview style is enabled.
 pub(crate) const fn is_module_docstring_newlines_enabled(context: &PyFormatContext) -> bool {
     context.is_preview()