BUG/TST/DEPR: Ensure dtype="category" always implies ordered=False & add tests

[ZanirP]

• closes DEPR: Make dtype="category" always imply ordered=False #61074
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

Issue: Previously, if a Series had ordered=True, using astype("category") would incorrectly preserve the ordering. This was inconsistent and against expectations.

Fix:

1. Now, dtype="category" always implies ordered=False.
2. If ordered=True before conversion, a deprecation warning is raised to inform users.
3. Tests have been updated to verify this new behavior.

[mroeschke]

Thanks for this PR.

While I support this change, I think we would need more discussion from the core team before proceeding with this deprecation

[mroeschke]

Going to close this PR pending discussion on the original issue. We can reopen once there is more consensus on moving forward here