MAINT: Add expiration notes for NumPy 2.0 removals

[mtsokol]

Hi @rgommers @ngoldbaum,

This PR adds a separate file and a migration notes mechanism (similar to previously removed functionalities, like "financial") for NumPy 2.0 expired functions and aliases.

Here I add notes for items that have been removed in Part 1 and Part 2 (excluding some niche internal enums that didn't have a single usage in libraries such as SciPy or Pandas).

[ngoldbaum]

This looks great!

I noticed that the AttributeError gets converted into an unhelpful ImportError if you do e.g. from numpy import NINF:

In [2]: np.NINF
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[2], line 1
----> 1 np.NINF

File ~/.pyenv/versions/3.10.9-debug/lib/python3.10/site-packages/numpy/__init__.py:349, in __getattr__(attr)
    346     raise AttributeError(__former_attrs__[attr])
    348 if attr in __expired_attributes__:
--> 349     raise AttributeError(
    350         f"`np.{attr}` was removed in NumPy 2.0 release. "
    351         f"{__expired_attributes__[attr]}"
    352     )
    354 raise AttributeError("module {!r} has no attribute "
    355                      "{!r}".format(__name__, attr))

AttributeError: `np.NINF` was removed in NumPy 2.0 release. Use `-np.inf` instead.

In [3]: from numpy import NINF
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
Cell In[3], line 1
----> 1 from numpy import NINF

ImportError: cannot import name 'NINF' from 'numpy' (/home/nathan/.pyenv/versions/3.10.9-debug/lib/python3.10/site-packages/numpy/__init__.py)

I spent a little time today trying to figure out a way to get a nicer ImportError, and I don't think there is. I also asked on the Python discourse: https://discuss.python.org/t/module-level-getattr-and-from-imports/32236

If there's nothing we can do about the from imports, I think it's still a big improvement to include the AttributeError, since someone might subsequent check a direct attribute access trying to debug the ImportError.

[ngoldbaum]

This looks good now, I think.

I'm going to propose a separate PR to generate better errors with from imports.

Thanks @mtsokol!