feat: better format dataset result download response

[nankolena]

Linked issue(s)

Resolves KOL-5941

Formatting the download_results() response better. Instead of having to rely on indexing the output such as:

response = download_results(dataset, model)
datapoints = response[0]
eval_config = response[1][0][0]
results = response[1][0][1]

We can now do:

response = download_results(dataset, model)
datapoints = response[0]
eval_config = response[1][0].eval_config
results = response[1][0].results

This change is backward compatible with the existing pattern of regular tuples, and the same change is applied to upload_results()

Updated API ref page:

What change does this PR introduce and why?

Please check if the PR fulfills these requirements

• [x] Include reference to internal ticket and/or GitHub issue "Fixes #NNNN" (if applicable)
• [x] Relevant tests for the changes have been added
• [x] Relevant docs have been added / updated

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.36%. Comparing base (96d960c) to head (246e01b). Report is 4 commits behind head on trunk.

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk     #597      +/-   ##
==========================================
- Coverage   94.40%   94.36%   -0.04%     
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  Files          85       85              
  Lines        5322     5327       +5     
  Branches      772      770       -2     
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+ Hits         5024     5027       +3     
- Misses        220      222       +2     
  Partials       78       78              

Flag	Coverage Δ
integration	74.77% <43.75%> (+0.02%)	:arrow_up:

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