GeezerVison

Brings Lib/configparser.py and Lib/test/test_configparser.py up to Ruff's
default rule set, which reported 72 findings across the two files. CPython's
own Ruff configuration only selects F401 and F811 for Lib/, so nothing
here was failing; the motivation is readability plus keeping the module
convergent with its PyPI backport, which lints with the defaults and would
otherwise need a per-file exemption for exactly these two files
(jaraco/configparser#73).

Four commits, each reviewable on its own:

1. f-strings (UP030, UP031, UP032) — the autofixable conversions,
   with the lines that would have exceeded 79 columns rewrapped by hand. The
   rendered strings are unchanged; %% escapes collapse to % as the %
   operator did.
2. Simplifications — C405, C408, C414, RUF019, RUF059, F841,
   SIM102, SIM117, and parenthesizing an implicit string concatenation
   inside a list literal (ISC004) so it does not read as a missing comma.
3. The remaining % sites that Ruff declines to autofix because the %d
   conversions are not provably integral. Converted by hand, keeping an
   explicit :d so a non-integer still raises rather than being coerced.
4. Imports, __all__, and ClassVar (I001, RUF022, RUF012).

The last one is the only part with a design decision in it. RUF012 wants
BOOLEAN_STATES annotated ClassVar, and the obvious spelling would import
typing at runtime — which this module deliberately avoids, per the
gh-117703 note above its imports. So it adds from __future__ import annotations and imports ClassVar only under TYPE_CHECKING, the same shape
Lib/tomllib/_parser.py and Lib/importlib/metadata/__init__.py use (both
also kept in sync with a PyPI backport). python -X importtime -c "import configparser" confirms typing stays out of the import graph. Deferring
annotations also lets Iterable['ParsingError'] drop its quotes (UP037).

That does make TYPE_CHECKING a module-level name, so it joins Error in
not_exported in the check__all__ test.

C901 on ExtendedInterpolation._interpolate_some (13 > 10) is the one
finding not fixed. It is a measurement, not a defect, and no small edit
satisfies it, so it gets # noqa: C901 # gh-159686; gh-159686 records why the
branching is inherent to the interpolation grammar and sketches a possible
refactoring, so the suppression is documented rather than silent.

With all four applied, both CPython's Ruff configuration and the default rule
set report no findings for either file, at py310 and py314 targets.
test_configparser, test_logging, test_collections, test___all__ and
test_pydoc pass.

NEWS entry added under Library; there is no user-visible behavior change.

• Issue: Modernize string formatting in configparser and its test module #159684

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