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

examples/py_custom_message_builder.py

@@ -51,9 +51,7 @@ print(person.extraData)
 print(type(person.extraData))
 print()
 
-person = addressbook_capnp.Person.new_message(
-    allocate_seg_callable=MemoryViewAllocator()
-)
+person = addressbook_capnp.Person.new_message(allocate_seg_callable=MemoryViewAllocator())
 
 person.init("extraData", 5)
 print(person.extraData)