feat: run playground tests in parallel (#1717)

- Adds a new button in the test playground to run tests in parallel
- Introduces `run_many_tests` to run playground tests in parallel using
futures!



https://github.com/user-attachments/assets/8652e643-9857-4468-8317-6b3ac20d162b


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> [!IMPORTANT]
> Adds functionality to run playground tests in parallel with a new
button and supporting logic for concurrent execution.
> 
>   - **Behavior**:
>     - Adds a button in `TestMenu.tsx` to run tests in parallel.
> - Implements `run_many_tests` in `mod.rs` to execute tests
concurrently using futures.
>   - **Functions**:
> - Introduces `useParallelRunTests` in `test-runner.ts` to manage
parallel test execution.
> - Updates `useRunTests` to support the new parallel execution logic.
>   - **Misc**:
>     - Adds `futures` dependency to `Cargo.toml` for async operations.
>     - Minor UI adjustments in `TestMenu.tsx` for the new button.
> 
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for 0b4851f. It will automatically
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Co-authored-by: ellipsis-dev[bot] <65095814+ellipsis-dev[bot]@users.noreply.github.com>
Co-authored-by: Aaron Villalpando <aaron@boundaryml.com>

Author: 3 people