[isort] support for configurable import section heading comments (#23151)

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## Summary

fixes #6371

- `settings.rs` - Added import_headings: FxHashMap<ImportSection,
String> field to Settings struct with default and display support
- `options.rs` - Added import_heading configuration option with
#[option] metadata, documentation, and TOML table syntax. Added
validation for unknown sections and mapping to Settings
- `mod.rs` - Core logic in format_import_block:
  - Collects all configured heading values as "# {heading}" strings
- Strips matching heading comments from ALL imports in each section
(handles reordering)
  - Inserts heading comments above each section after blank line logic
- `organize_imports.rs` - Extended fix range backward to include heading
comment lines above the first import, preventing duplication on fix
application

## Test Plan

Test Coverage (9 new tests, 156 total passing)

```
cargo test -p ruff_linter -- isort::tests
cargo test -p ruff_linter -- isort::tests::import_heading
```

| Test | Scenario |

|-------------------------------------------|------------------------------------------------------|
| import_heading.py | Basic unsorted imports get headings added |
| import_heading_already_present.py | Existing headings stripped and
re-added correctly |
| import_heading_already_correct.py | Properly sorted+headed imports
produce NO diagnostic |
| import_heading_unsorted.py | Completely unsorted imports get sorted
with headings |
| import_heading_with_no_lines_before.py | Interaction with
no_lines_before setting |
| import_heading_partial.py | Headings configured for only some sections
|
| import_heading_wrong_heading.py | Non-matching comments preserved as
regular comments |
| import_heading_single_section.py | Only one section present gets its
heading |
| import_heading_force_sort_within_sections.py | Works with
force_sort_within_sections |

---------

Co-authored-by: Brent Westbrook <36778786+ntBre@users.noreply.github.com>
Co-authored-by: Amethyst Reese <amethyst@n7.gg>

Author: 3 people

crates/ruff/tests/cli/snapshots/cli__lint__requires_python_extend_from_shared_config.snap

@@ -208,6 +208,7 @@ linter.isort.classes = []
 linter.isort.constants = []
 linter.isort.variables = []
 linter.isort.no_lines_before = []
+linter.isort.import_headings = {}
 linter.isort.lines_after_imports = -1
 linter.isort.lines_between_types = 0
 linter.isort.forced_separate = []

crates/ruff/tests/cli/snapshots/cli__lint__requires_python_no_tool.snap

@@ -210,6 +210,7 @@ linter.isort.classes = []
 linter.isort.constants = []
 linter.isort.variables = []
 linter.isort.no_lines_before = []
+linter.isort.import_headings = {}
 linter.isort.lines_after_imports = -1
 linter.isort.lines_between_types = 0
 linter.isort.forced_separate = []

crates/ruff/tests/cli/snapshots/cli__lint__requires_python_no_tool_preview_enabled.snap

@@ -212,6 +212,7 @@ linter.isort.classes = []
 linter.isort.constants = []
 linter.isort.variables = []
 linter.isort.no_lines_before = []
+linter.isort.import_headings = {}
 linter.isort.lines_after_imports = -1
 linter.isort.lines_between_types = 0
 linter.isort.forced_separate = []

crates/ruff/tests/cli/snapshots/cli__lint__requires_python_no_tool_target_version_override.snap

@@ -212,6 +212,7 @@ linter.isort.classes = []
 linter.isort.constants = []
 linter.isort.variables = []
 linter.isort.no_lines_before = []
+linter.isort.import_headings = {}
 linter.isort.lines_after_imports = -1
 linter.isort.lines_between_types = 0
 linter.isort.forced_separate = []

crates/ruff/tests/cli/snapshots/cli__lint__requires_python_pyproject_toml_above.snap

@@ -209,6 +209,7 @@ linter.isort.classes = []
 linter.isort.constants = []
 linter.isort.variables = []
 linter.isort.no_lines_before = []
+linter.isort.import_headings = {}
 linter.isort.lines_after_imports = -1
 linter.isort.lines_between_types = 0
 linter.isort.forced_separate = []

crates/ruff/tests/cli/snapshots/cli__lint__requires_python_pyproject_toml_above_with_tool.snap

@@ -210,6 +210,7 @@ linter.isort.classes = []
 linter.isort.constants = []
 linter.isort.variables = []
 linter.isort.no_lines_before = []
+linter.isort.import_headings = {}
 linter.isort.lines_after_imports = -1
 linter.isort.lines_between_types = 0
 linter.isort.forced_separate = []

crates/ruff/tests/cli/snapshots/cli__lint__requires_python_ruff_toml_above-2.snap

@@ -208,6 +208,7 @@ linter.isort.classes = []
 linter.isort.constants = []
 linter.isort.variables = []
 linter.isort.no_lines_before = []
+linter.isort.import_headings = {}
 linter.isort.lines_after_imports = -1
 linter.isort.lines_between_types = 0
 linter.isort.forced_separate = []

crates/ruff/tests/cli/snapshots/cli__lint__requires_python_ruff_toml_above.snap

@@ -208,6 +208,7 @@ linter.isort.classes = []
 linter.isort.constants = []
 linter.isort.variables = []
 linter.isort.no_lines_before = []
+linter.isort.import_headings = {}
 linter.isort.lines_after_imports = -1
 linter.isort.lines_between_types = 0
 linter.isort.forced_separate = []

crates/ruff/tests/cli/snapshots/cli__lint__requires_python_ruff_toml_no_target_fallback.snap

@@ -208,6 +208,7 @@ linter.isort.classes = []
 linter.isort.constants = []
 linter.isort.variables = []
 linter.isort.no_lines_before = []
+linter.isort.import_headings = {}
 linter.isort.lines_after_imports = -1
 linter.isort.lines_between_types = 0
 linter.isort.forced_separate = []

crates/ruff/tests/snapshots/show_settings__display_default_settings.snap

@@ -321,6 +321,7 @@ linter.isort.classes = []
 linter.isort.constants = []
 linter.isort.variables = []
 linter.isort.no_lines_before = []
+linter.isort.import_headings = {}
 linter.isort.lines_after_imports = -1
 linter.isort.lines_between_types = 0
 linter.isort.forced_separate = []