core: cleanup deprecations, exclude from type checking and show runtime warnings

among affected things:

- core.common.assert_never
- core.common.cproperty
- core.common.isoparse
- core.common.mcachew
- core.common.the
- core.common.tzdatetime
- core.compat.sqlite_backup

my/core/tests/test_cachew.py

@@ -10,7 +10,7 @@ def test_cachew() -> None:
 
     settings.ENABLE = True  # by default it's off in tests (see conftest.py)
 
-    from my.core.common import mcachew
+    from my.core.cachew import mcachew
 
     called = 0
 
@@ -36,7 +36,7 @@ def test_cachew_dir_none() -> None:
     settings.ENABLE = True  # by default it's off in tests (see conftest.py)
 
     from my.core.cachew import cache_dir
-    from my.core.common import mcachew
+    from my.core.cachew import mcachew
     from my.core.core_config import _reset_config as reset
 
     with reset() as cc:

my/core/tests/test_get_files.py

@@ -6,7 +6,6 @@ from typing import TYPE_CHECKING
 import zipfile
 
 from ..common import get_files
-from ..compat import windows
 from ..kompress import CPath, ZipPath
 
 import pytest
@@ -56,8 +55,9 @@ def test_single_file() -> None:
     '''
     assert get_files('/tmp/hpi_test/file.ext') == (Path('/tmp/hpi_test/file.ext'),)
 
+    is_windows = os.name == 'nt'
     "if the path starts with ~, we expand it"
-    if not windows:  # windows doesn't have bashrc.. ugh
+    if not is_windows:  # windows doesn't have bashrc.. ugh
         assert get_files('~/.bashrc') == (Path('~').expanduser() / '.bashrc',)