ENH: Add dropna parameter to Series.unique() (fixes #61209)

[sahermuhamed1]

• 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.

Changes:

• Added dropna parameter to Series.unique() (default=True)
• Ensured backward compatibility
• Added comprehensive test coverage

Notes:

• Changes split into logical commits:
  1. Core functionality (ENH)
  2. Test coverage (TST)

[mroeschke]

Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in the main branch, address any review comments and/or failing tests, and we can reopen.