gh-40799: Move typing imports to TYPE_CHECKING block and enable relevant ruff checks
    
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Plus some related import cleanups.

This avoid importing modules that are only imported for type checking at
runtime. This should speed up how long the modules take load at runtime,
but I didn't measure it. This will be more important as more of the Sage
codebase gets type annotations over time.

### 📝 Checklist

<!-- Put an `x` in all the boxes that apply. -->

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.
    
URL: #40799
Reported by: Vincent Macri
Reviewer(s): Tobias Diez, Vincent Macri

Author: Release Manager

.github/workflows/lint.yml

@@ -35,7 +35,7 @@ jobs:
       if: (success() || failure()) && steps.deps.outcome == 'success'
       run: |
         uv run --frozen --only-group lint -- ruff check --output-format github --ignore E402,E721,E731,E741,E742,E743,F401,F402,F403,F405,F821,F841,I001,PLC0206,PLC0208,PLC1802,PLC2401,PLC3002,PLC0415,PLE0302,PLR0124,PLR0402,PLR0911,PLR0912,PLR0913,PLR0915,PLR1704,PLR1711,PLR1714,PLR1716,PLR1733,PLR1736,PLR2004,PLR5501,PLW0120,PLW0211,PLW0602,PLW0603,PLW0642,PLW1508,PLW1510,PLW1641,PLW2901,PLW3301
-        uv run --frozen --only-group lint -- ruff check --output-format github --preview --select E111,E115,E21,E221,E222,E225,E227,E228,E25,E271,E272,E275,E302,E303,E305,E306,E401,E502,E701,E702,E703,E71,W291,W293,W391,W605 src/sage/
+        uv run --frozen --only-group lint -- ruff check --output-format github --preview --select E111,E115,E21,E221,E222,E225,E227,E228,E25,E271,E272,E275,E302,E303,E305,E306,E401,E502,E701,E702,E703,E71,W291,W293,W391,W605,TC src/sage/
 
     - name: Code style check with relint
       if: (success() || failure()) && steps.deps.outcome == 'success'

conftest.py

@@ -11,8 +11,7 @@
 import inspect
 import sys
 import warnings
-from pathlib import Path
-from typing import Any, Iterable, Optional
+from typing import Any, Iterable, Optional, TYPE_CHECKING
 
 import pytest
 from _pytest.doctest import (
@@ -32,6 +31,9 @@
 )
 from sage.doctest.parsing import SageDocTestParser, SageOutputChecker
 
+if TYPE_CHECKING:
+    from pathlib import Path
+
 
 class SageDoctestModule(DoctestModule):
     """

pyproject.toml

@@ -241,6 +241,7 @@ select = [
   "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
+  "TC", # flake8-type-checking - https://docs.astral.sh/ruff/rules/#flake8-type-checking-tc
 ]
 
 [tool.ruff.lint.per-file-ignores]

src/sage/combinat/cluster_algebra_quiver/mutation_type.py

@@ -23,7 +23,8 @@
 from copy import copy
 from pathlib import Path
 import pickle
-from typing import Any, Iterator
+from typing import Any
+from collections.abc import Iterator
 
 
 from sage.misc.cachefunc import cached_function

src/sage/combinat/combinat.py

@@ -123,7 +123,6 @@
 # ****************************************************************************
 from __future__ import annotations
 
-from collections.abc import Iterator
 
 from sage.arith.misc import bernoulli, factorial
 from sage.combinat.combinat_cython import _stirling_number2
@@ -138,6 +137,10 @@
 from sage.rings.rational_field import QQ
 from sage.structure.element import Element
 from sage.structure.sage_object import SageObject
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from collections.abc import Iterator
 
 lazy_import('sage.interfaces.maxima_lib', 'maxima')
 lazy_import('sage.libs.pari', 'pari')

src/sage/combinat/dyck_word.py

@@ -77,7 +77,6 @@
 #                  https://www.gnu.org/licenses/
 # ****************************************************************************
 from __future__ import annotations
-from collections.abc import Iterator
 
 from .combinat import CombinatorialElement, catalan_number
 from sage.combinat.combinatorial_map import combinatorial_map
@@ -97,6 +96,10 @@
 from sage.combinat.set_partition import SetPartitions
 from sage.misc.latex import latex
 from sage.misc.lazy_import import lazy_import
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from collections.abc import Iterator
 
 lazy_import('sage.combinat.alternating_sign_matrix', 'AlternatingSignMatrices')
 

src/sage/combinat/interval_posets.py

@@ -30,7 +30,6 @@
 #                  https://www.gnu.org/licenses/
 # ****************************************************************************
 from __future__ import annotations
-from collections.abc import Iterator
 
 from sage.categories.enumerated_sets import EnumeratedSets
 from sage.categories.finite_enumerated_sets import FiniteEnumeratedSets
@@ -58,6 +57,10 @@
 from sage.structure.richcmp import richcmp, op_NE, op_EQ
 from sage.structure.unique_representation import UniqueRepresentation
 from sage.graphs.digraph import DiGraph
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from collections.abc import Iterator
 
 lazy_import('sage.combinat.dyck_word', 'DyckWords')
 

src/sage/combinat/parking_functions.py

@@ -63,7 +63,6 @@
 #                  https://www.gnu.org/licenses/
 # ****************************************************************************
 from __future__ import annotations
-from collections.abc import Iterator
 
 from sage.rings.integer import Integer
 from sage.rings.rational_field import QQ
@@ -80,6 +79,10 @@
 from sage.categories.sets_with_grading import SetsWithGrading
 from sage.structure.parent import Parent
 from sage.structure.unique_representation import UniqueRepresentation
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from collections.abc import Iterator
 
 
 def is_a(x, n=None) -> bool:

src/sage/combinat/permutation.py

@@ -239,10 +239,9 @@
 #                  https://www.gnu.org/licenses/
 # ****************************************************************************
 from __future__ import annotations
-from collections.abc import Iterator
 import itertools
 import operator
-from typing import Iterable
+from typing import TYPE_CHECKING
 
 from sage.arith.misc import factorial, multinomial
 from sage.categories.finite_enumerated_sets import FiniteEnumeratedSets
@@ -271,6 +270,9 @@
 from sage.structure.element import Element, get_coercion_model
 from sage.structure.unique_representation import UniqueRepresentation
 
+if TYPE_CHECKING:
+    from collections.abc import Iterable, Iterator
+
 lazy_import('sage.combinat.rsk', ['RSK', 'RSK_inverse'])
 lazy_import('sage.combinat.tableau', 'Tableau')
 lazy_import('sage.combinat.words.finite_word', 'evaluation_dict')

src/sage/combinat/plane_partition.py

@@ -25,8 +25,7 @@
 # ****************************************************************************
 
 from __future__ import annotations
-from typing import NewType
-from collections.abc import Iterator
+from typing import NewType, TYPE_CHECKING
 
 from sage.structure.richcmp import richcmp, richcmp_method
 from sage.categories.finite_enumerated_sets import FiniteEnumeratedSets
@@ -44,6 +43,9 @@
 from sage.sets.family import Family
 from sage.sets.non_negative_integers import NonNegativeIntegers
 
+if TYPE_CHECKING:
+    from collections.abc import Iterator
+
 lazy_import('sage.modules.free_module_element', 'vector')