MAINT: a nicer way to detect a module is deprecated in DTModule

[ev-br]

The try-except-pass stanza was bothering me every time I saw it.

Turns out it was to filter out modules which are deprecated, meaning they emit a DeprecationWarning on an attribute access. Consider

In [1]: from scipy.constants import constants      # deprecated submodule constants.constants

In [2]: constants.zetta      # DeprecationWarning
<ipython-input-5-835b60441caf>:1: DeprecationWarning: Please import `zetta` from the `scipy.constants` namespace; the `scipy.constants.constants` namespace is deprecated and will be removed in SciPy 2.0.0.
  constants.zetta
Out[5]: 1e+21

Note however that non-existent attributes still raise an AttributeError, only with a helpful error message:

In [3]: constants.tapas                 # non-existent attr: AttributeError w/ special error message
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[2], line 1
----> 1 constants.tapas

File ~/repos/scipy/scipy/build-install/lib/python3.10/site-packages/scipy/constants/constants.py:51, in __getattr__(name)
     50 def __getattr__(name):
---> 51     return _sub_module_deprecation(sub_package="constants", module="constants",
     52                                    private_modules=["_constants"], all=__all__,
     53                                    attribute=name)

File ~/repos/scipy/scipy/build-install/lib/python3.10/site-packages/scipy/_lib/deprecation.py:42, in _sub_module_deprecation(sub_package, module, private_modules, all, attribute, correct_module)
     39     correct_import = f"scipy.{sub_package}"
     41 if attribute not in all:
---> 42     raise AttributeError(
     43         f"`scipy.{sub_package}.{module}` has no attribute `{attribute}`; "
     44         f"furthermore, `scipy.{sub_package}.{module}` is deprecated "
     45         f"and will be removed in SciPy 2.0.0."
     46     )
     48 attr = getattr(import_module(correct_import), attribute, None)
     50 if attr is not None:

AttributeError: `scipy.constants.constants` has no attribute `tapas`; furthermore, `scipy.constants.constants` is deprecated and will be removed in SciPy 2.0.0.

[ev-br]

Merged to test scipy/scipy#20127 on CI. A post-merge review would be valuable @Sheila-nk

[Sheila-nk]

LGTM! 👏