Comment all Ruff rule codes; tweak formatting

This adds comments to all specific Ruff rules suppressed in
pyproject.toml (most of which are global but one is for the tests
only). Some already had such comments but now all do.

This also harmonizes the toml formatting style with the rest of
pyproject.toml.

pyproject.toml

@@ -54,24 +54,28 @@ exclude = [
 # Enable Pyflakes `E` and `F` codes by default.
 lint.select = [
     "E",
-    "W", # see: https://pypi.org/project/pycodestyle
-    "F", # see: https://pypi.org/project/pyflakes
-#    "I", #see: https://pypi.org/project/isort/
-#    "S", # see: https://pypi.org/project/flake8-bandit
-#    "UP", # see: https://docs.astral.sh/ruff/rules/#pyupgrade-up
+    "W",     # See: https://pypi.org/project/pycodestyle
+    "F",     # See: https://pypi.org/project/pyflakes
+    # "I",   # See: https://pypi.org/project/isort/
+    # "S",   # See: https://pypi.org/project/flake8-bandit
+    # "UP",  # See: https://docs.astral.sh/ruff/rules/#pyupgrade-up
 ]
 lint.extend-select = [
-    #"A",    # see: https://pypi.org/project/flake8-builtins
-    "B",    # see: https://pypi.org/project/flake8-bugbear
-    "C4",   # see: https://pypi.org/project/flake8-comprehensions
-    "TCH004", # see: https://docs.astral.sh/ruff/rules/runtime-import-in-type-checking-block/
+    # "A",     # See: https://pypi.org/project/flake8-builtins
+    "B",       # See: https://pypi.org/project/flake8-bugbear
+    "C4",      # See: https://pypi.org/project/flake8-comprehensions
+    "TCH004",  # See: https://docs.astral.sh/ruff/rules/runtime-import-in-type-checking-block/
 ]
 lint.ignore = [
-    "E203",
-    "E731", # Do not assign a `lambda` expression, use a `def`
+    "E203",  # Whitespace before ':'
+    "E731",  # Do not assign a `lambda` expression, use a `def`
 ]
 lint.ignore-init-module-imports = true
-lint.unfixable = ["F401"]
+lint.unfixable = [
+    "F401",  # Module imported but unused
+]
 
 [tool.ruff.lint.per-file-ignores]
-"test/**" = ["B018"]
+"test/**" = [
+    "B018",  # useless-expression
+]