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_get_data_view.py

@@ -197,12 +197,10 @@ def test_view_keeps_message_alive(all_types):
     view = msg.get_data_as_view("dataField")
     new_ref_count = sys.getrefcount(msg)
 
-    assert (
-        new_ref_count > initial_ref_count
-    ), f"View failed to hold reference to Message! (Old: {initial_ref_count}, New: {new_ref_count})"
-    print(
-        f"\n[Ref Check] Success: Ref count increased from {initial_ref_count} to {new_ref_count}"
+    assert new_ref_count > initial_ref_count, (
+        f"View failed to hold reference to Message! (Old: {initial_ref_count}, New: {new_ref_count})"
     )
+    print(f"\n[Ref Check] Success: Ref count increased from {initial_ref_count} to {new_ref_count}")
 
     del msg
     gc.collect()