Fix slice index for benchmark-8 2D

[charlesbmi]

Introduction

Scenario 2 is based on benchmark 8 of Aubry et al. (2022). NDK provides a 2D variant that is supposed to correspond to the slice through the transducer.

Changes

Fixes the slice index for benchmark 8's 2D variant to match the paper description:

Using 1-based indexing, the center of the source (rear of the bowl or center of the piston) relative to the output grid was positioned at... [1, 171, 191] for benchmark 8.

This also happens to be the middle slice: .shape[2] // 2. The 3-D mask.shape is (451, 341, 381)

TODO:

• re-direct this PR towards main once Implementing new API for NDK #122 lands.

[NewtonSander]

@charlesincharge I took the liberty of rebasing your PR as I've fixed the issue that caused the CI to fail in the base branch

[charlesbmi]

Thanks!