Replace black and flake8 with ruff for linting and formatting

- Remove .flake8; add [tool.ruff] and [tool.ruff.format] config in pyproject.toml
  (line-length 120, excludes, ignore list, per-file-ignores, mccabe complexity)
- Update GitHub workflow lint job to run `ruff check .` and `ruff format --check .`
- Swap black and flake8 for ruff in requirements.txt and Pipfile
- Change capnp/__init__.py to ruff-style noqa comment
- Move max-complexity into [tool.ruff.lint.mccabe], lint options into [tool.ruff.lint]
- Add per-file-ignores for capnp/__init__.py (F401, F403, F405), remove inline noqa
- Run ruff format across codebase (24 files) for consistent style

test/test_schema.py

@@ -40,15 +40,11 @@ def test_annotations(annotations):
     assert annotation.value.struct.as_struct(annotations.AnnotationStruct).test == 100
 
     annotation = annotations.TestAnnotationThree.schema.node.annotations[0]
-    annotation_list = annotation.value.list.as_list(
-        capnp._ListSchema(annotations.AnnotationStruct)
-    )
+    annotation_list = annotation.value.list.as_list(capnp._ListSchema(annotations.AnnotationStruct))
     assert annotation_list[0].test == 100
     assert annotation_list[1].test == 101
 
     annotation = annotations.TestAnnotationFour.schema.node.annotations[0]
-    annotation_list = annotation.value.list.as_list(
-        capnp._ListSchema(capnp.types.UInt16)
-    )
+    annotation_list = annotation.value.list.as_list(capnp._ListSchema(capnp.types.UInt16))
     assert annotation_list[0] == 200
     assert annotation_list[1] == 201