sagemathgh-37452: Add config for ruff (sagemath#36503, unbundled)
    
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Author: @mkoeppe, based on @tobiasdiez's config in sagemath#36503.

Adding a configuration for the ruff linter as proposed in sagemath#36503 is
timely and uncontroversial.

However, sagemath#36503 bundled this gratuitously with the controversial design
of creating a `pyproject.toml` file in SAGE_ROOT.

`pyproject.toml` -- by definition in PEP 518, PEP 621 -- marks a
directory as a Python project, i.e., the source directory of a Python
distribution package
(sagemath#36503 (comment)).
Generalizing the use of `pyproject.toml` to "[non-package
projects](https://peps.python.org/pep-0735/#motivation)" is still
subject to discussion in the Python community in [PEP
735](https://peps.python.org/pep-0735/) (Nov 2023).

**The scope of PRs should be chosen to minimize friction, not to
maximize friction.**
sagemath#36726 (comment)
Here we remove the artificial friction from the gratuitous bundling, by
configuring ruff in `ruff.toml` instead. Configuration in ruff.toml and
pyproject.toml has equal validity / standing per [ruff
documentation](https://docs.astral.sh/ruff/configuration/#config-file-
discovery). And this is the location of most of our other linter
configuration files.

Reference on previous common denominator PRs:
sagemath#36666 (comment),
sagemath#36666 (comment),
sagemath#36572 (comment),
sagemath#36960 (comment),
sagemath#36960 (comment), ...

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- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

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URL: sagemath#37452
Reported by: Matthias Köppe
Reviewer(s): Giacomo Pope, Matthias Köppe

Author: Release Manager

.devcontainer/devcontainer.json

@@ -22,13 +22,12 @@
 		"vscode": {
 			"extensions": [
 				"guyskk.language-cython",
-				"ms-python.isort",
 				"ms-toolsai.jupyter",
 				"ms-python.vscode-pylance",
-				"ms-python.pylint",
 				"ms-python.python",
 				"lextudio.restructuredtext",
-				"trond-snekvik.simple-rst"
+				"trond-snekvik.simple-rst",
+				"charliermarsh.ruff"
 			]
 		}
 	}

.vscode/extensions.json

@@ -2,6 +2,7 @@
 	// List of extensions which should be recommended for developers when a workspace is opened for the first time.
 	// See https://go.microsoft.com/fwlink/?LinkId=827846 to learn about workspace recommendations.
 	"recommendations": [
-		"ms-python.python"
+		"ms-python.python",
+		"charliermarsh.ruff"
 	],
 }

.vscode/settings.json

@@ -24,11 +24,6 @@
         "--doctest-modules"
     ],
     "python.testing.unittestEnabled": false,
-    "python.linting.pycodestyleEnabled": true,
-    "python.linting.enabled": true,
-    // The following pycodestyle arguments are the same as the pycodestyle-minimal
-    // tox environnment, see the file SAGE_ROOT/src/tox.ini
-    "python.linting.pycodestyleArgs": ["--select= E111,E21,E222,E225,E227,E228,E25,E271,E303,E305,E306,E401,E502,E701,E702,E703,E71,E72,W291,W293,W391,W605"],
     "cSpell.words": [
         "furo",
         "Conda",

ruff.toml

@@ -0,0 +1,14 @@
+# https://docs.astral.sh/ruff/configuration/#config-file-discovery
+
+# Assume Python 3.9
+target-version = "py39"
+
+select = [
+    "E", # pycodestyle errors - https://docs.astral.sh/ruff/rules/#error-e
+    "F", # pyflakes - https://docs.astral.sh/ruff/rules/#pyflakes-f
+    "I", # isort - https://docs.astral.sh/ruff/rules/#isort-i
+    "PL", # pylint - https://docs.astral.sh/ruff/rules/#pylint-pl
+]
+ignore = [
+    "E501", # Line too long - hard to avoid in doctests, and better handled by black.
+]