GH-132983: Remove subclassing support from zstd types

[AA-Turner]

cc @Rogdham

For what it's worth, bz2 and lzma's decompressor subclassing fail on creation:

>>> import bz2
>>> class D(bz2.BZ2Decompressor): pass
... 
Traceback (most recent call last):
  File "<python-input-18>", line 1, in <module>
    class D(bz2.BZ2Decompressor): pass
TypeError: type '_bz2.BZ2Decompressor' is not an acceptable base type

>>> import lzma
>>> class D(lzma.LZMADecompressor): pass
... 
Traceback (most recent call last):
  File "<python-input-19>", line 1, in <module>
    class D(lzma.LZMADecompressor): pass
TypeError: type '_lzma.LZMADecompressor' is not an acceptable base type

• Issue: Implement PEP 784 - Adding Zstandard to the Python standard library #132983

[Rogdham]

LGTM, I also confirmed it works as intended.

I just noticed the case difference between zstdcompressor_type_spec and ZstdDecompressor_type_spec (and same for …_slots), but maybe it's for an other PR?

[AA-Turner]

See #133674, which does the rename.

[miss-islington-app]

Thanks @AA-Turner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-133762 is a backport of this pull request to the 3.14 branch.