Defer inspect import to reduce import time by ~24%

Move `import inspect` from module level in `_compat.py` and
`_make.py` into the functions that use it. Lazy-load `converters`
and `validators` submodules from `attr/__init__.py` and
`attrs/__init__.py` since they trigger class building (which
invokes inspect) at import time.

inspect is only used in three places, all at class-build time:
- _compat._AnnotationExtractor.__init__() for signature extraction
- _make.py line 709 for __attrs_pre_init__ arg detection
- _make.py line 931 for cached_property return annotations

Benchmark (Python 3.13, PYTHONDONTWRITEBYTECODE=1, 50 runs):
- Before: 85.0ms ± 20.4ms
- After:  64.7ms ± 12.0ms
- Improvement: ~20ms (24%)

All 1385 tests pass.

Author: KRRT7

src/attr/__init__.py

@@ -7,7 +7,7 @@
 from functools import partial
 from typing import Callable, Literal, Protocol
 
-from . import converters, exceptions, filters, setters, validators
+from . import exceptions, filters, setters
 from ._cmp import cmp_using
 from ._config import get_run_validators, set_run_validators
 from ._funcs import asdict, assoc, astuple, has, resolve_types
@@ -78,13 +78,23 @@ class AttrsInstance(Protocol):
 ]
 
 
+_LAZY_SUBMODULES = {"converters", "validators"}
+
+
 def _make_getattr(mod_name: str) -> Callable:
     """
     Create a metadata proxy for packaging information that uses *mod_name* in
     its warnings and errors.
     """
 
     def __getattr__(name: str) -> str:
+        if name in _LAZY_SUBMODULES:
+            import importlib
+
+            mod = importlib.import_module(f".{name}", mod_name)
+            globals()[name] = mod
+            return mod
+
         if name not in ("__version__", "__version_info__"):
             msg = f"module {mod_name} has no attribute {name}"
             raise AttributeError(msg)

src/attr/_compat.py

@@ -1,6 +1,5 @@
 # SPDX-License-Identifier: MIT
 
-import inspect
 import platform
 import sys
 import threading
@@ -46,6 +45,8 @@ class _AnnotationExtractor:
     __slots__ = ["sig"]
 
     def __init__(self, callable):
+        import inspect  # noqa: PLC0415
+
         try:
             self.sig = inspect.signature(callable)
         except (ValueError, TypeError):  # inspect failed
@@ -55,6 +56,8 @@ def get_first_param_type(self):
         """
         Return the type annotation of the first argument if it's not empty.
         """
+        import inspect  # noqa: PLC0415
+
         if not self.sig:
             return None
 
@@ -68,6 +71,8 @@ def get_return_type(self):
         """
         Return the return type if it's not empty.
         """
+        import inspect  # noqa: PLC0415
+
         if (
             self.sig
             and self.sig.return_annotation is not inspect.Signature.empty

src/attr/_make.py

@@ -6,7 +6,6 @@
 import contextlib
 import copy
 import enum
-import inspect
 import itertools
 import linecache
 import sys
@@ -705,6 +704,8 @@ def __init__(
         if self._has_pre_init:
             # Check if the pre init method has more arguments than just `self`
             # We want to pass arguments if pre init expects arguments
+            import inspect  # noqa: PLC0415
+
             pre_init_func = cls.__attrs_pre_init__
             pre_init_signature = inspect.signature(pre_init_func)
             self._pre_init_has_args = len(pre_init_signature.parameters) > 1
@@ -920,6 +921,8 @@ def _create_slots_class(self):
         # To know to update them.
         additional_closure_functions_to_update = []
         if cached_properties:
+            import inspect  # noqa: PLC0415
+
             class_annotations = _get_annotations(self._cls)
             for name, func in cached_properties.items():
                 # Add cached properties to names for slotting.

src/attrs/__init__.py

@@ -25,7 +25,7 @@
 from attr._make import ClassProps
 from attr._next_gen import asdict, astuple, inspect
 
-from . import converters, exceptions, filters, setters, validators
+from . import exceptions, filters, setters
 
 
 __all__ = [