Always place non-relative imports after relative imports (#10669)

## Summary

When `relative-imports-order = "closest-to-furthest"` is set, we should
_still_ put non-relative imports after relative imports. It's rare for
them to be in the same section, but _possible_ if you use
`known-local-folder`.

Closes https://github.com/astral-sh/ruff/issues/10655.

## Test Plan

New tests.

Also sorted this file:

```python
from ..models import ABC
from .models import Question
from .utils import create_question
from django_polls.apps.polls.models import Choice
```

With both:

- `isort view.py`
- `ruff check view.py --select I --fix`

And the following `pyproject.toml`:

```toml
[tool.ruff.lint.isort]
order-by-type = false
relative-imports-order = "closest-to-furthest"
known-local-folder = ["django_polls"]

[tool.isort]
profile = "black"
reverse_relative = true
known_local_folder = ["django_polls"]
```

I verified that Ruff and isort gave the same result, and that they
_still_ gave the same result when removing the relevant setting:

```toml
[tool.ruff.lint.isort]
order-by-type = false
known-local-folder = ["django_polls"]

[tool.isort]
profile = "black"
known_local_folder = ["django_polls"]
```

crates/ruff_linter/resources/test/fixtures/isort/separate_local_folder_imports.py

@@ -3,3 +3,5 @@ import ruff
 import leading_prefix
 import os
 from . import leading_prefix
+from .. import trailing_prefix
+from ruff import check

crates/ruff_linter/src/rules/isort/mod.rs

@@ -471,6 +471,31 @@ mod tests {
         Ok(())
     }
 
+    #[test_case(Path::new("separate_local_folder_imports.py"))]
+    fn known_local_folder_closest(path: &Path) -> Result<()> {
+        let snapshot = format!("known_local_folder_closest_{}", path.to_string_lossy());
+        let diagnostics = test_path(
+            Path::new("isort").join(path).as_path(),
+            &LinterSettings {
+                isort: super::settings::Settings {
+                    known_modules: KnownModules::new(
+                        vec![],
+                        vec![],
+                        vec![pattern("ruff")],
+                        vec![],
+                        FxHashMap::default(),
+                    ),
+                    relative_imports_order: RelativeImportsOrder::ClosestToFurthest,
+                    ..super::settings::Settings::default()
+                },
+                src: vec![test_resource_path("fixtures/isort")],
+                ..LinterSettings::for_rule(Rule::UnsortedImports)
+            },
+        )?;
+        assert_messages!(snapshot, diagnostics);
+        Ok(())
+    }
+
     #[test_case(Path::new("case_sensitive.py"))]
     fn case_sensitive(path: &Path) -> Result<()> {
         let snapshot = format!("case_sensitive_{}", path.to_string_lossy());

crates/ruff_linter/src/rules/isort/snapshots/ruff_linter__rules__isort__tests__known_local_folder_closest_separate_local_folder_imports.py.snap

@@ -0,0 +1,27 @@
+---
+source: crates/ruff_linter/src/rules/isort/mod.rs
+---
+separate_local_folder_imports.py:1:1: I001 [*] Import block is un-sorted or un-formatted
+  |
+1 | / import sys
+2 | | import ruff
+3 | | import leading_prefix
+4 | | import os
+5 | | from . import leading_prefix
+6 | | from .. import trailing_prefix
+7 | | from ruff import check
+  |
+  = help: Organize imports
+
+ℹ Safe fix
+  1 |+import os
+1 2 | import sys
+  3 |+
+  4 |+import leading_prefix
+  5 |+
+2 6 | import ruff
+3   |-import leading_prefix
+4   |-import os
+5 7 | from . import leading_prefix
+6 8 | from .. import trailing_prefix
+7 9 | from ruff import check

crates/ruff_linter/src/rules/isort/snapshots/ruff_linter__rules__isort__tests__known_local_folder_separate_local_folder_imports.py.snap

@@ -8,6 +8,8 @@ separate_local_folder_imports.py:1:1: I001 [*] Import block is un-sorted or un-f
 3 | | import leading_prefix
 4 | | import os
 5 | | from . import leading_prefix
+6 | | from .. import trailing_prefix
+7 | | from ruff import check
   |
   = help: Organize imports
 
@@ -20,6 +22,7 @@ separate_local_folder_imports.py:1:1: I001 [*] Import block is un-sorted or un-f
 2 6 | import ruff
 3   |-import leading_prefix
 4   |-import os
-5 7 | from . import leading_prefix
-
-
+  7 |+from .. import trailing_prefix
+5 8 | from . import leading_prefix
+6   |-from .. import trailing_prefix
+7 9 | from ruff import check

crates/ruff_linter/src/rules/isort/snapshots/ruff_linter__rules__isort__tests__separate_local_folder_imports.py.snap

@@ -8,18 +8,22 @@ separate_local_folder_imports.py:1:1: I001 [*] Import block is un-sorted or un-f
 3 | | import leading_prefix
 4 | | import os
 5 | | from . import leading_prefix
+6 | | from .. import trailing_prefix
+7 | | from ruff import check
   |
   = help: Organize imports
 
 ℹ Safe fix
-  1 |+import os
-1 2 | import sys
-  3 |+
-2 4 | import ruff
-  5 |+
-3 6 | import leading_prefix
-4   |-import os
-  7 |+
-5 8 | from . import leading_prefix
-
-
+   1  |+import os
+1  2  | import sys
+   3  |+
+2  4  | import ruff
+   5  |+from ruff import check
+   6  |+
+3  7  | import leading_prefix
+4     |-import os
+   8  |+
+   9  |+from .. import trailing_prefix
+5  10 | from . import leading_prefix
+6     |-from .. import trailing_prefix
+7     |-from ruff import check

crates/ruff_linter/src/rules/isort/sorting.rs

@@ -69,6 +69,7 @@ impl<'a> From<String> for NatOrdStr<'a> {
 pub(crate) enum Distance {
     Nearest(u32),
     Furthest(Reverse<u32>),
+    None,
 }
 
 #[derive(Debug, Copy, Clone, PartialOrd, Ord, PartialEq, Eq)]
@@ -101,17 +102,20 @@ impl<'a> ModuleKey<'a> {
         style: ImportStyle,
         settings: &Settings,
     ) -> Self {
-        let level = level.unwrap_or_default();
-
         let force_to_top = !name.is_some_and(|name| settings.force_to_top.contains(name)); // `false` < `true` so we get forced to top first
 
         let maybe_length = (settings.length_sort
             || (settings.length_sort_straight && style == ImportStyle::Straight))
-            .then_some(name.map(str::width).unwrap_or_default() + level as usize);
+            .then_some(
+                name.map(str::width).unwrap_or_default() + level.unwrap_or_default() as usize,
+            );
 
-        let distance = match settings.relative_imports_order {
-            RelativeImportsOrder::ClosestToFurthest => Distance::Nearest(level),
-            RelativeImportsOrder::FurthestToClosest => Distance::Furthest(Reverse(level)),
+        let distance = match level {
+            None | Some(0) => Distance::None,
+            Some(level) => match settings.relative_imports_order {
+                RelativeImportsOrder::ClosestToFurthest => Distance::Nearest(level),
+                RelativeImportsOrder::FurthestToClosest => Distance::Furthest(Reverse(level)),
+            },
         };
 
         let maybe_lowercase_name = name.and_then(|name| {