chore: add Ruff and apply formatting across codebase

Introduce ruff lint/format config, expand .gitignore, and reformat Python sources.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_resume.py

@@ -13,7 +13,6 @@ from imagepipeline.core.resume import (
 )
 from imagepipeline.core.step import StepDefinition
 from imagepipeline.modules.imagemagick_grayscale import ImageMagickGrayscale
-from imagepipeline.modules.registry import get_module
 from imagepipeline.modules.rembg import RembgModule
 from imagepipeline.utils.gmic import finalize_gmic_output, split_gmic_command
 from tests.conftest import make_png
@@ -124,7 +123,9 @@ class TestExpectedOutputFilenames:
 
 class TestPipelineResume:
     @pytest.mark.skipif(not shutil.which("magick"), reason="ImageMagick not installed")
-    def test_continue_skips_completed_steps(self, input_dir: Path, output_base: Path, capsys) -> None:
+    def test_continue_skips_completed_steps(
+        self, input_dir: Path, output_base: Path, capsys
+    ) -> None:
         with Pipeline(
             name="resume_test",
             input_dir=input_dir,
@@ -195,9 +196,7 @@ class TestPipelineResume:
             verbose=True,
             existing_outputs={"input_bokeh": external},
         ) as p:
-            reused = p.step(
-                "imagemagick_grayscale", inputs="input", step_id="input_bokeh"
-            )
+            reused = p.step("imagemagick_grayscale", inputs="input", step_id="input_bokeh")
             p.step("imagemagick_grayscale", inputs=reused)
             root = p.run()