Update `initialize_q_batch` methods to return both candidates and the corresponding acquisition values

[saitcakmak]

Summary: As titled. This avoids the need to re-compute the acquisition values after sub-selecting in cases where they are needed.

Differential Revision: D64333367

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This pull request was exported from Phabricator. Differential Revision: D64333367

[codecov[bot]]

Codecov Report

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

Project coverage is 99.98%. Comparing base (85d8996) to head (f2cbf99). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2571 +/- ## ======================================= Coverage 99.98% 99.98% ======================================= Files 195 195 Lines 17116 17122 +6 ======================================= + Hits 17113 17119 +6 Misses 3 3 ```

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@saitcakmak has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

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This pull request was exported from Phabricator. Differential Revision: D64333367

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D64333367

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@saitcakmak merged this pull request in pytorch/botorch@b79dfb0faba89cd0410c16199be4c5ceed40fdeb.