Fix type errors flagged by ty 0.0.43

[gaborbernat]

The scheduled type / type-min checks broke once ty bumped to 0.0.43 (we pin ty>=0.0.19, so CI pulls the latest). This fixes the failures, removes the Windows-runner deprecation notice without churning required-check names, and cleans up every # ty: ignore that has a real fix.

1. ty 0.0.43 failures

Three new diagnostics from stricter type-variable handling:

• src/tox/config/of_type.py — ty now narrows the negative branch of callable() on a Callable[[], T] | T union to object. Instead of the old blanket # ty: ignore[call-top-callable] + cast("T", ...), each branch now casts the value to its precise factory signature before invoking it, so the call is type-checked against a known signature.
• tests/config/loader/test_toml_loader.py — factory_na returned NoReturn, so ty inferred Loader.load's type variable as Never, collapsing type[Never] | UnionType to UnionType. Made factory_na generic over the same V so the variable binds from of_type.

2. Windows runner notice + version-less check names

GitHub is redirecting windows-2025 to windows-2025-vs2026 by 2026-06-15. The job names embed ${{ matrix.os }}, and those strings are the repository ruleset's required-check contexts — so naively renaming the runner would have permanently blocked merges.

Instead the matrix os entry is split into a versioned runner image and a bare display name:

os:
  - { image: ubuntu-24.04, name: ubuntu }
  - { image: windows-2025-vs2026, name: windows }
  - { image: macos-15, name: macos }
# name:     test ${{ matrix.py }} on ${{ matrix.os.name }}
# runs-on:  ${{ matrix.os.image }}

Jobs now run on the new image but report stable, version-less check names (test 3.14 on windows, tox env type on ubuntu, …) that won't churn on future image bumps. The repository ruleset's required status checks were updated to the new names accordingly. Applied to check.yaml and weekly.yaml; the release/admin workflows are single ubuntu jobs with no OS in their names and were left unchanged.

3. # ty: ignore cleanup — 8 removed via real type fixes

Location	Was suppressed	Fix
execute/local_sub_process	ov.WriteFile unresolved	declared WriteFile in typestubs/_overlapped.pyi
pip/req/file.py	dict-key invalid-argument-type	annotated lookup as dict[type, int]
virtual_env/package/pyproject.py	.value unresolved	cast to ConfigConstantDefinition[str] (always registered via add_constant)
session/env_select.py ×2	group invalid-assignment + completer unresolved	typed group as _ActionsContainer; declared completer on _CliEnvAction
config/loader/toml/__init__.py ×3	list[of_type] / dict[...] invalid-type-form	built via types.GenericAlias (identical runtime object, plain value expression)
config/cli/parser.py ×2	list[action.type] invalid-type-form	same GenericAlias construction

Left in place (no clean fix)

• Upstream ty bugs (issue-linked): add_config no-matching-overload ×7 (wrong inference of function literals off subclass-of types astral-sh/ty#2428 — fires only when default's callable form and post_process are both present, even with fully-typed args; collapsing the overloads breaks inference differently), plus tox4: (regression) unable to run interactive commands #2374, In parallel mode, tox marks skipped interpreters as succeded. #1495, Support - prefix for commands exit code ignore #2586.
• Intentional error-path tests: test_sets.py passes deliberately-wrong arguments to assert the raised error.
• Runtime dynamic patterns: monkeypatching stdlib Thread.start, wrapping argparse instance methods, attaching metadata attrs to base argparse.Action, and a dynamic Literal[tuple(...)].

Verification

tox r -e type (ty 0.0.43) clean; ruff clean; targeted suites (config loader/CLI, env_select, req file, package pyproject, sets) all pass.

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