fix(sdk): invalid order of items returned by VotePollsByEndDateDriveQuery

[lklimek]

Issue being fixed or feature implemented

VotePollsByEndDateDriveQuery supports order_ascending field for the requests.
Unfortunately, internally we use BTreeMap that always orders items in ascending order.

There is a rev() method to reverse iteration, but it's not intuitive - as user requested reversed objects, standard iter() should return them in reverse order.

What was done?

Implemented OrderedBTreeMap that allows iterating over items in reverse order and used it in VotePollsGroupedByTimestamp.

Note: this only fixes Sdk-side of the issue. Drive still returns items in invalid order.

How Has This Been Tested?

Test fetch::contested_resource_polls_by_ts::vote_polls_by_ts_order is green.

Breaking Changes

None

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have added "!" to the title and described breaking changes in the corresponding section if my code contains any
• I have made corresponding changes to the documentation if needed

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[lklimek]

Refactored to use Vec<> instead of BTreeMap, included in #1906