A symlink always pointing to the most recent experiment's artifact directory should exist

For each experiment, there exists a `latest` symlink that always points to the most recent experiment's artifact directory. For example:

```
.data/
├─ 01-validate-incremental-building/
│ ├─ 20231030T095641-653fc429/
│ ├─ 20240311T121101-65ef3b25/
│ ├─ latest/
├─ 03-validate-local-build-caching-different-locations/
│ ├─ 20240311T121415-65ef3be7/
│ ├─ latest/
```

We should additionally add a symlink directly beneath `.data` that always points to the most recent experiment's artifact directory across all experiments. For example:

```
.data/
├─ latest/
├─ 01-validate-incremental-building/
│ ├─ 20231030T095641-653fc429/
│ ├─ 20240311T121101-65ef3b25/
│ ├─ latest/
├─ 03-validate-local-build-caching-different-locations/
│ ├─ 20240311T121415-65ef3be7/
│ ├─ latest/
```

If `03-validate-local-build-caching-different-locations/20240311T121415-65ef3be7` was the most recently run experiment across all experiments, then `.data/latest/` would be a symlink of `.data/03-validate-local-build-caching-different-locations/20240311T121415-65ef3be7/`.

This is convenient when you know you know what you want to inspect is the most recent experiment's artifacts. This can also help simplify automation scenarios when you want to grab the receipt file of the latest experiment run because you do not need to know the name of the script to grab the receipt.

Inspect the experiment workflow that creates each experiment's `latest` symlink and trace how the newest artifact directory is selected. Run experiments covering multiple experiment directories, then verify that `.data/latest` points to the artifact directory of the most recently run experiment while existing per-experiment links still work.

Written by the indexing model from the issue text.