DOC: Update DataFrame.stack() docstring for 3.0 deprecations

[anandvenugopal-tech]

Updated the docstring for DataFrame.stack() to reflect pandas 3.0 behavior.

• Marked parameters dropna, sort, and future_stack as deprecated

• Updated descriptions to clarify that these parameters no longer have any effect

• Updated examples and notes where necessary

• closes #xxxx (Replace xxxx with the GitHub issue number)

• 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.

• If I used AI to develop this pull request, I prompted it to follow AGENTS.md.

[anandvenugopal-tech]

Hi,
I’ve updated the docstring as requested. All docstring validation, pre-commit hooks, typing, code checks, and documentation builds are now passing successfully.
The only remaining failures are unrelated unit tests, which seem to come from the CI environment and are not affected by this documentation-only change.
Please let me know if any further adjustments are needed.
Thank you!