feat: add competition ranking to leaderboard

[virratanasangpunth]

No description provided.

[malandis]

Couple changes upon review:

• An oversight from the previous PR: I should have re-used FetchResponse for get_rank instead of making a new response type. Could you refactor get_competition_rank to use FetchResponse instead of a new response type here as well?
• Also refactor get_rank to use the same

[virratanasangpunth]

GH Actions seem to checkout older code revisions of this PR.... odd....

[virratanasangpunth]

https://github.com/momentohq/client-sdk-rust/actions/runs/13294066680/job/37121603883?pr=439

It's complaning about:

error[E0061]: this method takes 1 argument but 2 arguments were supplied
   --> tests/leaderboard/mod.rs:415:14
    |
415 |             .get_competition_rank([0, 1, 2, 3, 4], Some(Order::Ascending))
    |              ^^^^^^^^^^^^^^^^^^^^                  ---------------------- unexpected argument #2 of type `std::option::Option<momento::leaderboard::Order>`

but that doesn't match the code in this PR: 5d07ce6#diff-fd78100889d055010c44e3f81caf0225a1545b419395f83c7823dfd764eee13fR415

        let response = leaderboard
            .send_request(GetCompetitionRankRequest::new([0, 1, 2, 3, 4]).order(Order::Ascending))
            .await?;

[malandis]