Add update_member and get_members_xlsx methods

[alistair0adams]

Added two methods

1. update_member() which will POST updated member data back to Spond
2. get_members_xlsx() which will download the Excel sheet that can be manually downloaded from the Spond website. This can easily then be converted into a Dataframe.

[elliot-100]

Thanks for this @alistair0adams .

Are you OK to add the missing return annotation? Should be JSONDict.

[alistair0adams]

JSONDict annotation added

[elliot-100]

Sorry @alistair0adams have been on other projects. Will try to test in next 1-2 weeks.

[Olen]

Thanks @alistair0adams — preparing a 1.2.1 release sweep and would love to bring these methods in. Before merging, this PR needs a quick refresh:

1. Rebase against main — the branch is currently flagged as conflicting after recent merges.
2. Docstring fixups:
   • update_member: "Updated memberi" typo (extra i).
   • update_member: references get_personb() — should be get_person().
3. Add a test for at least one of the two methods. The existing tests/test_spond.py::TestExportMethod::test_get_export is a close shape for get_members_xlsx and easy to adapt; update_member can follow test_change_response's mocking pattern.

If you're short on time and want to land just the cleanup + rebase, I'm happy to take #197 over by pushing to your branch (or open a follow-up PR that picks your commit). Let me know what works best.