feat: support concurrency in base sampling strategy

[jakelorocco]

Pull Request

Issue

Fixes N/A; builds on previously closed PR (#240)

Description

Adds concurrency to our base sampling strategy. We lacked a way to concurrently sample and were only able to sample iteratively. The sample() now manages distinct generators. subsample_iteration replaces the actual sampling code that was previously in sample().

The total number of sampling iterations is now loop_budget * concurrency_budget. Concurrency budget is the breadth of the tree, loop_budget is the depth of the tree. At any time only concurrency_budget number of sampling iterations are running.

Testing

• Tests added to the respective file if code was changed
• New code has 100% coverage if code was added
• Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

Attribution

• AI coding assistants used; marked in commit

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Adding a new component, requirement, sampling strategy, or tool?

If your PR adds or modifies one of the types below, check the matching box. A checklist of type-specific review items will be posted as a comment.

• Component
• Requirement
• Sampling Strategy
• Tool

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