Process isolation is not working on MPS device

Setting up the launcher to `process` on an MPS device causes the benchmark to be stuck permanently on “Sending report to main process.”

Steps to reproduce:
Run this configuration on an MPS device (Mac M-series).
```
defaults:
- benchmark
- scenario: inference
- **launcher: process # launcher: inline works**
- backend: pytorch
- _base_
- _self_

name: pytorch_bert

scenario:
latency: true
memory: true
input_shapes:
batch_size: 1
sequence_length: 128

backend:
device: mps
no_weights: true
model: bert-base-uncased
```
(example adapted from `pytorch_bert.yaml`)

Temporary Solution: set to `launcher: inline`

Remarks: `launcher.start_method: fork` does not also work on mac