Move back to flake8, remove ruff

Choice of linter toolchain is a matter for project developers. `ruff`
was pushed by an external contributor, and was accepted to hopefully
improve interest/engagement in maintenance.

However, there was no particular reason to use `ruff` and it puts us
in the position of opting out of a lot of configs rather than opting
in to what we want.

flake8 also offers a plugin framework which allows for checks like
`flake8-typing-as-t` to be easily added post-hoc.

In addition to flake8, reapply isort and pyupgrade, and add slyp.

.flake8

@@ -0,0 +1,4 @@
+[flake8]
+exclude = .git,.tox,__pycache__,.eggs,dist,.venv*,docs,build
+max-line-length = 88
+extend-ignore = W503,W504,E203

.pre-commit-config.yaml

@@ -18,20 +18,33 @@ repos:
   hooks:
   - id: black
     language_version: python3
+- repo: https://github.com/PyCQA/isort
+  rev: 5.12.0
+  hooks:
+    - id: isort
+- repo: https://github.com/asottile/pyupgrade
+  rev: v3.15.0
+  hooks:
+    - id: pyupgrade
+      args: ["--py37-plus"]
+- repo: https://github.com/PyCQA/flake8
+  rev: 6.1.0
+  hooks:
+    - id: flake8
+      additional_dependencies:
+        - 'flake8-bugbear==23.9.16'
+        - 'flake8-comprehensions==3.14.0'
+        - 'flake8-typing-as-t==0.0.3'
+- repo: https://github.com/sirosen/slyp
+  rev: 0.1.2
+  hooks:
+    - id: slyp
 - repo: https://github.com/codespell-project/codespell
   rev: v2.2.5
   hooks:
     - id: codespell
       additional_dependencies:
         - tomli
-- repo: https://github.com/astral-sh/ruff-pre-commit
-  rev: v0.0.291
-  hooks:
-    - id: ruff
-- repo: https://github.com/abravalheri/validate-pyproject
-  rev: v0.14
-  hooks:
-    - id: validate-pyproject
 - repo: https://github.com/tox-dev/pyproject-fmt
   rev: 1.2.0
   hooks:

pyproject.toml

@@ -59,83 +59,6 @@ nose2 = "nose2:discover"
 [tool.setuptools.dynamic]
 version = {attr = "nose2.__version__"}
 
-[tool.ruff]
-select = [
-  "B",       # flake8-bugbear
-  "C4",      # flake8-comprehensions
-  "C90",     # McCabe cyclomatic complexity
-  "E",       # pycodestyle
-  "EXE",     # flake8-executable
-  "F",       # Pyflakes
-  "I",       # isort
-  "ICN",     # flake8-import-conventions
-  "INT",     # flake8-gettext
-  "PLE",     # Pylint errors
-  "PLR091",  # Pylint Refactor just for max-args, max-branches, etc.
-  "PYI",     # flake8-pyi
-  "RSE",     # flake8-raise
-  "RUF",     # Ruff-specific rules
-  "TCH",     # flake8-type-checking
-  "TID",     # flake8-tidy-imports
-  "UP",      # pyupgrade
-  "W",       # pycodestyle
-  "YTT",     # flake8-2020
-  # "A",     # flake8-builtins
-  # "ANN",   # flake8-annotations
-  # "ARG",   # flake8-unused-arguments
-  # "BLE",   # flake8-blind-except
-  # "COM",   # flake8-commas
-  # "D",     # pydocstyle
-  # "DJ",    # flake8-django
-  # "DTZ",   # flake8-datetimez
-  # "EM",    # flake8-errmsg
-  # "ERA",   # eradicate
-  # "FBT",   # flake8-boolean-trap
-  # "G",     # flake8-logging-format
-  # "INP",   # flake8-no-pep420
-  # "ISC",   # flake8-implicit-str-concat
-  # "N",     # pep8-naming
-  # "NPY",   # NumPy-specific rules
-  # "PD",    # pandas-vet
-  # "PGH",   # pygrep-hooks
-  # "PIE",   # flake8-pie
-  # "PT",    # flake8-pytest-style
-  # "PTH",   # flake8-use-pathlib
-  # "Q",     # flake8-quotes
-  # "RET",   # flake8-return
-  # "S",     # flake8-bandit
-  # "SIM",   # flake8-simplify
-  # "SLF",   # flake8-self
-  # "T10",   # flake8-debugger
-  # "T20",   # flake8-print
-  # "TRY",   # tryceratops
-]
-ignore = [
-  "B904",
-  "RUF005",
-  "RUF012",
-  "RUF100"
-]
-target-version = "py37"
-
-[tool.ruff.isort]
-known-third-party = [
-  "coverage",
-  "mock",
-]
-
-[tool.ruff.mccabe]
-max-complexity = 15
-
-[tool.ruff.pylint]
-max-args = 9
-max-branches = 15
-max-statements = 66
-
-[tool.ruff.per-file-ignores]
-"nose2/tests/*" = ["B011"]
-# FIXME: resolving these could change behavior -- do it in a separate
-#        cleanup and note it in the changelog
-"nose2/plugins/loader/*.py" = ["B004"]
-"nose2/plugins/mp.py" = ["UP031"]
-"nose2/tests/functional/support/such/test_regression_same_havings.py" = ["EXE001"]
+[tool.isort]
+profile = "black"
+known_third_party = ["coverage", "mock"]